Multielectrode Electrosurgical Instrument

ABSTRACT

An improved electrosurgical instrument includes a body having more than two electrodes with at least two electrodes having alternating current power supplied to them provide a bipolar alternating current configuration and employ a means other than electrode spacing for reducing or preventing accumulation of eschar. The electrodes are separated from each other using electrically insulating materials such that electric current does not flow between at least two of the bipolar alternating current electrodes unless they contact at least one other electrically conductive medium, such as patient tissue. The conductor edge portion and insulation layer each have geometric shapes and composition to reduce or eliminate the production of smoke and eschar and reduce tissue damage. The outer profile of the insulation layer and conductive element are configured to facilitate the flow of electrosurgical decomposition products away from the conductor edge where they are formed.

This application claims the benefit of priority to U.S. ProvisionalApplication 60/695,692 entitled Multielectrode ElectrosurgicalInstrument filed Jun. 30, 2005, the entire contents of which are herebyincorporated by reference. This application also claims the benefit ofpriority as a continuation-in-part to U.S. application Ser. No.11/185,668 entitled Multielectrode Electrosurgical Instrument filed Jul.20, 2005, which claims the benefit of priority to U.S. ProvisionalApplication 60/589,508 filed Jul. 20, 2004, the entire contents of bothof which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to surgical methods and apparatus, andmore particularly to applying electrosurgical power to a tissue site toachieve a predetermined surgical effect.

BACKGROUND OF THE INVENTION

The potential applications and recognized advantages of employingelectrical energy in surgical procedures continue to increase. Inparticular, for example, electrosurgical techniques are now being widelyemployed to provide significant localized surgical advantages in open,laparoscopic, and arthroscopic applications, relative to surgicalapproaches that use mechanical cutting such as scalpels.

Electrosurgical techniques typically entail the use of a hand-heldinstrument that contains one or more electrically conductive elementsthat transfer alternating current electrical power operating at radiofrequency (RF) to tissue at the surgical site, a source of RF electricalpower, and an electrical return path device, commonly in the form of areturn electrode pad attached to the patient away from the surgical site(i.e., a monopolar system configuration) or a return electrodepositionable in bodily contact at or immediately adjacent to thesurgical site (i.e., a bipolar system configuration). The time-varyingvoltage produced by the RF electrical power source yields apredetermined electrosurgical effect, such as tissue cutting orcoagulation.

During electrosurgical procedures electric current flows through one ormore conductive elements, the active electrodes, and transferselectrical current to tissues, often with coincident sparks or arcs ofelectricity occurring between one or more electrodes and tissues. Theoverall process causes heating of tissue and the electrode metal. Tissueheating causes tissues to break into fragments or otherwise change intomaterials that generally differ physically and chemically from thetissue before it was affected by electrosurgery. The tissue changes atthe surgical site, such as charring, interfere with normal metabolicprocesses and, for example, kill tissues that remain at the surface ofincisions. The changes in tissues caused by electrosurgical energy, suchas killing parts of tissues, are known to interfere with healing at thesurgical site.

Beyond damaging tissue at the surgical site, conventional electrosurgeryhas other drawbacks which limit its applicability or increase the costsand duration of procedures. Induced heating of tissues and electrodescauses smoke plumes to issue from the tissue. Smoke obscures the fieldof view and hinders surgical procedures and is also a known healthhazard. Controlling smoke once it has formed is problematic, requiringthe evacuation of large volumes of air in order to capture anappreciable fraction of the smoke with wands that are close to thesurgical site where they are in the way, and adds costs in bothadditional equipment and labor.

The induced heating also generally causes tissue that has been alteredby electrosurgery to adhere to and partially coat electrosurgicalelectrodes. The tissue fragments that adhere to electrodes and coat theelectrodes is called “eschar.” The coatings on blades that form fromtissue and tissue fragments are typically rich in carbon and containvarious compounds that tend to make the coatings electrically conductivewhen energized by the type of power used for electrosurgical procedures.Eschar inhibits the effectiveness of electrosurgical devices and mustfrequently be removed, hindering surgical procedures.

Despite advances in the field, electrosurgical blades continue to sufferfrom one or more of the problems of producing smoke, having materialsfrom tissues coat the blades, and damaging tissue. Therefore, a needexists to improve performance in each of these areas. Historically,electrosurgical blades have generally not given consideration to thechemical reaction environment and conditions that occur where theelectrosurgical energy interacts with tissue by considering factors suchas the propensity of tissue to become trapped in regions that lead toprolonged residence times at reactive conditions that lead to producingsmoke and materials that coat blades to form eschar. Likewise, prior artelectrosurgical blades did not consider the conductive pathways that canbe formed by tissue fragments adhering to blades and the effects thatthese built-up conductive pathways have on producing smoke, producingmore materials that can further coat blades, and the effects that thesehave during electrosurgery.

SUMMARY

Various embodiments provide an apparatus, and methods for using theapparatus, in electrosurgery that controls the environment in whichelectrosurgical energy transfers to tissue.

The various embodiments employ blade geometry, blade composition or acombination of blade geometry and composition to reduce or prevent smokeproduction, eschar accumulations, or tissue damage. The embodimentsfocus electrosurgical energy to a small amount of tissue for a shortduration compared to the amount of tissue and duration than is customaryduring electrosurgery using conventional technology. Various embodimentsyield less eschar accumulation on the electrosurgical instrument byproviding an exterior surface of the instrument with a shape thatfacilitates movement of tissue decomposition products away from theactive region of the conductive element The active region is a region onthe conductive element where electrosurgical energy transfers from theblade to tissue. In some embodiments, the tapered configuration includesan electrically conductive element with a tapered section. In someembodiments, the tapered configuration includes configuring aninsulating layer with a tapered section. In various embodiments,insulation on the conductive element has a surface free energy thatreduces the propensity for electrosurgical decomposition products(defined herein) to stick to the surface. In various embodiments, theshape of the blade minimizes the duration that the active region is nearany particular portion of tissue as the blade is moved through tissue asduring an incision.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitutepart of this specification, illustrate embodiments of the invention,and, together with the general description given above and the detaileddescription given below, serve to explain features of the invention.

FIG. 1 portrays a system schematic with a general multielectrode bladehaving active, passive, and return electrodes.

FIG. 2 portrays a system schematic with a general multielectrode bladehaving active, passive, and return electrodes with an activation switch.

FIG. 3 portrays a system schematic with a multielectrode blade havingactive, passive, and return electrodes with DC power derived from the RFpower.

FIG. 4 portrays a system schematic with a multielectrode blade havingactive and return electrodes with DC power derived from the RF power.

FIG. 5 portrays a system schematic with a multielectrode blade havingactive and return electrodes with DC power derived from the RF powerwith an activation switch.

FIG. 6 illustrates a side view of an electrosurgical instrument havingan electrode blade.

FIG. 7 portrays a cross section of a multielectrode blade having active,passive, and return electrodes with a substantially flat contact face.

FIG. 8 portrays a cross section of a multielectrode blade having active,passive, and return electrodes with a convex contact face.

FIG. 9 portrays a cross section of a multielectrode blade having active,passive, and return electrodes with a convex contact face with electrodeedges exposed.

FIG. 10 portrays a perspective view of a portion of a multielectrodeblade with insulation cut away to show active, passive, and returnelectrodes tapered to a convex contact face having electrode edgesexposed.

FIG. 11 portrays a cross section of a multielectrode blade havingactive, passive, and return electrodes with a convex contact face havingelectrode edges exposed and an adjacent concave surface.

FIG. 12 portrays a cross-section of a blade that has been insulatedwhereby the outer taper to the edge is defined by a single smooth curveat the conductor edge.

FIG. 13 portrays a magnified section of the region where electrosurgicalenergy interacts with tissue for the blade illustrated in FIG. 1.

FIG. 14 portrays a magnified section of the region where electrosurgicalenergy interacts with tissue for the blade illustrated in FIG. 2 andshows the blade depth and half-width.

FIG. 15 portrays a cross-section of a blade with a conductive elementthat has a concave taper that has been insulated whereby the outer taperto the edge is not defined by a single smooth curve at the conductoredge.

FIG. 16 portrays a cross-section of a blade with a conductive elementthat has a substantially flat taper that has been insulated whereby theouter taper to the edge is not defined by a single smooth curve at theconductor edge.

FIG. 17 portrays a cross-section of a blade with a conductive elementthat has a concave taper that has been insulated whereby the outer taperto the edge is not defined by a single smooth curve at the conductoredge and that shows the insulation angle.

FIG. 18 portrays a cross-section of a blade with a conductive elementwhere the outer taper to the edge is defined by a single smooth curve atthe conductor edge showing the insulation angle.

FIG. 19 portrays a cross-section of a blade with a conductive elementthat has a concave taper that has an overall profile that has a taperthat transitions from curved to approximately flat at the edge of theblade.

FIG. 20 portrays a cross section of a blade having a conductive elementthat has a concave taper and a concave overall taper to an edge.

FIG. 21 portrays a side view of a blade with two exposed edges at anobtuse angle.

FIG. 22 portrays a side view of blade with two exposed edges at anobtuse angle in relation to making a tissue incision.

FIG. 23 portrays a side view of blade with two exposed edges at an acuteangle in relation to making a tissue incision.

FIG. 24 portrays a side view of blade with one exposed edge in relationto making a tissue incision.

FIGS. 25A-C illustrates a multielectrode electrosurgical blade accordingto an embodiment.

FIG. 26 illustrates an electrosurgical instrument including a holder andblade according to an embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The various embodiments will be described in detail with reference tothe accompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

As used herein, the terms “about” or “approximately” for any numericalvalues or ranges indicates a suitable dimensional tolerance that allowsthe part or collection of components to function for its intendedpurpose as described herein. Also, as used herein, the terms “patient”,“tissue” and “subject” refer to any human or animal subject and are notintended to limit the systems or methods to human use, although use ofthe subject invention on a human patient represents a specificembodiment.

All devices that may be used to produce a predetermined surgical effectby applying RF power to tissue may be referred to herein aselectrosurgical “blades” due to their function of partial or completeremoval of one or more parts of tissue (including changing the structuresuch as by at least partially denaturing or decomposing), regardless oftheir size, shape, or other properties. Use of the term “blade” hereinis not intended to restrict the description or any embodiment to aparticular shape or configuration. While various embodiments pertain togenerally planar elements which may resemble a conventional scalpelblade, other embodiments encompass element configurations which aredissimilar from conventional blades, including, for example, needle,hook and curved configurations.

Reference herein to the purpose and effects of electrosurgical devicesas producing “a predetermined surgical effect” encompasses all potentialeffects generated during electrosurgery. The predetermined surgicaleffect include, but are not limited to: causing a partial or completeseparation of one or more tissue structures or types, including, but notlimited to making electrosurgical incisions; cause partial or completeremoval of one or more parts of a tissue; changing the structure oftissue, such by at least partially denaturing or decomposing tissue;cutting; hemostasis (such as by inducing coagulation); tissue welding;tissue sealing, and tissue shrinking. Commonly, multiple predeterminedsurgical effects occur simultaneously, such as cutting and hemostasisboth occurring as incisions are made.

Although they may have various forms, all sources of RF power used topower electrosurgical blades will be referred to herein aselectrosurgical units and abbreviated by ESU.

The terms “electrode” and “conductive elements” are used interchangeablyherein to refer to similar structures without intending to communicateor imply a difference in structure or limitation on any embodiment orclaim of the present invention.

Electrosurgical devices come in two common varieties, monopolar andbipolar. Monopolar electrosurgical blades connect to an ESU using a wirewhile a separate return pad is connected to the ESU by another wire.Bipolar electrosurgical blades connect a set of one or more activeelectrodes to the ESU with one or more wires and connect another set ofone or more return electrodes to the ESU with one or more other wires,wherein the active electrode or electrodes and return electrodes orelectrode are connected together so that RF energy may be conveyedthrough one or more conductive media that contact at least one tissuewith such connections between electrodes being either permanent ortemporary, such as by being separately inserted into a clamping deviceor a handle with such connection being fixed or moveable, such as asliding connection.

The present inventors have recognized that reducing the amount of energyapplied to tissue reduces tissue breakdown and that the amount ofapplied energy can be reduced by reducing the exposure toelectrosurgical power (where electrosurgical power is the rate at whichelectrosurgical energy is applied) either by reducing the power level,the time of exposure to electrosurgical power, or by reducing both thepower level and the time of exposure. Various embodiments reduce theenergy to which tissue is exposed by proper selection of blade geometry,blade materials, and the amount of power used.

More generally in this regard, energy discharge from electrosurgicalinstruments may be in the form of electrical energy and/or thermalenergy. Electrical energy is transferred whenever the electricalresistance of a region between an electrosurgical instrument and tissuecan be broken down by the voltage of the electrosurgical power. Thermalenergy is transferred when thermal energy that has accumulated in theelectrosurgical instrument overcomes the thermal resistance between theinstrument and the tissue (i.e. due to temperature differencestherebetween) and is transferred to tissue by conduction, radiationand/or convection. Transferring electrosurgical energy to tissue occursat portions of the electrosurgical instrument which cause the desiredsurgical effect, such as forming an incision. Such portions of theinstrument are called functional areas. All other portions of theelectrosurgical instrument are nonfunctional, and transfer ofelectrosurgical energy to tissue from these portions should beminimized. Electrosurgical energy may be transferred to tissue withoutdirect contact with the functional area by means of electrical sparksand radiative and convective heat transfer. As used herein, the term“contact” relating to the position of blades or electrodes near tissueencompasses both actual contact and positioning of a functional areaclose enough to tissue for transfer of electrosurgical energy to occur.

Pyrolysis is the breakdown of molecules into smaller moieties by theaction of heat (physical fragmentation), typically followed bysubsequent recombination of these thermal fragments to form largerspecies. As used herein, the term “electropyrolysis” refers to theprocess whereby electrical energy in the form of sparks or arcsinteracts with tissue to break down tissue constituents by heat,electron interactions with materials, photon interactions withmaterials, or any combination of these.

In general terms, electrosurgery is the process by which high voltage(e.g., voltages greater than about 100 volts) electrical power isapplied to tissue to achieve a predetermined surgical effect. Suchvoltages are typically employed as high frequency (e.g., frequenciesgreater than about 5 kHz) and most commonly use frequencies greater thanabout 100 kHz to reduce neuromuscular stimulation. The energy istransferred to tissue at the surgical site using one or more electrodes.Electrical energy is transferred as well as thermal energy which comesfrom electrodes becoming hot as electrical power moves through them,producing I²R power losses which manifest themselves as heat, some ofwhich is transferred to tissue via conduction, radiation, andconvection. As used herein, the term “electrosurgical energy” refers toall of the energy transferred to tissue during electrosurgery,regardless of form or transfer mechanism, and including both electricaland thermal energy.

Without restriction to any particular theory of operation regarding itsform or method of use, the following descriptions of processes duringelectrosurgery are provided to illustrate one or more candidateprocesses that could be present during electrosurgery to facilitatesubsequent descriptions of the various embodiments.

Tissue breaks down where sparks or hot metal contact it. This breakdownof tissue is believed to be caused by rapid heating of tissue whereelectrosurgical energy, principally electrical sparks and thermal energyfrom hot metal, contacts tissue and electropyrolysis and hydrolysis lysetissue constituents.

During electrosurgery a variety of reaction products are produced.Electropyrolysis is believed to be a cause of tissue breakdown duringelectrosurgery. One result of electropyrolysis during electrosurgery isthe production of hot water and steam which promote hydrolysis oftissues. For example, electropyrolysis and hydrolysis are believed tobreak down proteins and produce a range of products, including cyclicand linear polypeptide materials. Electropyrolysis is also believed tobe the process by which electrosurgery is able to cut or otherwise breakdown tissues that have a cellular structure (e.g., muscle tissue) aswell as tissues that do not have a cellular structure (e.g., collagenfibrils in ligaments).

Beyond electropyrolysis products, other electrosurgery products are alsoformed. Most notable are changes in state in which materials changetheir state (e.g., steam forming when water changes from liquid to gas)but are otherwise not changed chemically. During electrosurgery someproducts have altered structure, but otherwise retain their chemicalidentity, such as when proteins denature and then refold into shapesdifferent from those prior to denaturation. During electrosurgery someproducts retain their chemical structure and state, but changephysically in other ways (e.g., air being heated so that its specificvolume increases).

Finally, some electrosurgery processes can cause materials, such ascellular contents or viral particles, to be liberated or moved with astream of other materials, such as being conveyed by flowing steam orhot air produced during electrosurgery.

Collectively, all of the materials produced or altered duringelectrosurgery, including those from electropyrolysis, change of state,change of structure, change of volume, and liberation are referred toherein as the “products of electrosurgery,” “electrosurgicaldecomposition products,” or “electrosurgical products”. The collectionof processes that break down or alter tissues during electrosurgery arereferred to here as electrosurgical tissue decomposition processes.

Some of the resulting materials form smoke or steam and some of theresulting materials form substances that stick to blades. Whenelectrosurgery is performed in a gaseous environment, such as air orcarbon dioxide, particularly when incisions are made, a common resultusing conventional technology is a smoke plume. The smoke plume isbelieved to consist primarily of pyrolysis and electropyrolysisproducts, including steam and hot air along with materials such ascellular contents and other entrained materials.

When electrosurgery is performed, including when incisions are made,some of the products of electrosurgery form deposits on electrodescontacting or in close proximity to tissue. These deposits, calledeschar, are believed to begin forming when sticky materials, such asdenatured proteins, adhere to electrode surfaces. Other materials mayalso be mixed in with the sticky materials. As electrosurgery proceeds,thermal energy continues to pyrolyze these materials on the electrodesleading to the production of substances having a higher carbon:hydrogencontent than the starting materials. Some resulting materials conductelectricity at the voltages used, perhaps due to the presence of ionsfrom salts or by having high carbon contents, and form an electricallyconductive coating on the blade, even if the blades surface is coatedwith an insulating coating. Therefore, eschar formation on the outsideof an insulated electrode that has, for example, only an edge exposed,can have an electrically active area that extends from the exposed edgebecause of conductive eschar deposits forming on the blade's surface andbeing in electrical contact with the exposed edge. This conductivedeposit can expose more tissue to prolonged exposure to electricalenergy.

Prior to the present invention, bipolar blades suffered from therequirement that the electrodes be close enough together so that currentwould reliably pass into tissue but not be so close together as to allowshort circuiting to occur though a bridge of conducing material, such ascarbonaceous material formed from thermally decomposed tissue products.Such deposits of thermally decomposed tissue products are called eschar.Eschar readily forms in the high temperature environment local toelectrosurgical blades. When electrodes are placed far enough apart toprevent short circuiting by eschar it becomes difficult to ensure thatboth active and return electrodes contact tissue. When the electrodesare close enough to ensure that both active and return electrodescontact tissue the rapid formation of short circuiting bridges ensues.

Prior art for bipolar electrosurgery blades have replaced the return padwith one or more electrodes on the blade itself. The additionalelectrode(s) are connected to the ESU using a wire. The electrical pathis generally described as coming from the ESU, to one electrode on theblade, through patient tissue, into the other electrode on the blade,and then back to the ESU. All of the prior art for bipolar blades hastwo or more electrodes, all of which are connected to the ESU such thatthey all experience the same voltage differences with such voltagedifferences either being direct current or alternating current and nevera combination of the two types of electrical energy. For example, U.S.Pat. No. 164,184 for a bipolar electrosurgical device describes using apair of conductors spirally wound onto a rubber probe body in which theconductors are embedded. The device is not used to make incisions anduses direct current supplied from a battery to apply the same voltagedifference to all electrodes. A bipolar electrosurgical device describedin U.S. Pat. No. 1,983,669 has a pair of conductors twisted around aninsulator that is powered by high frequency (i.e., alternating current)energy. U.S. Pat. No. 4,011,872 shows an electrosurgical devicefeaturing two, three or four electrodes all connected to the same radiofrequency energy source by a single conductor.

The electrodes may take on a variety of configurations, as describedusing the following exemplary prior art. In U.S. Pat. No. 3,970,088,U.S. Pat. No. 3,987,795, and U.S. Pat. No. 4,043,342, (collectively “theMorrison patents”), electrode configurations are disclosed wherein thesurface areas of the active and return electrodes are substantiallydifferent. The Morrison patents disclose using a porous materialsurrounding electrodes to enhance stable startup. The Morrison patentsfurther disclose using multiple electrodes in which all of theelectrodes are connected to the ESU such that the RF power is applied toall of the electrodes. U.S. Pat. No. 4,202,337 and U.S. Pat. No.4,228,800 disclose bipolar blade configurations with split electrodes inwhich all of the electrodes are connected to the ESU such that RF poweris applied to all of the electrodes. The '337 and '800 patents furtherdisclose bipolar blades that insert into a handle that has electricalcontacts that provide electrical connections to the ESU such that a pairof side electrodes are shorted together and act as the return electrodewith a center electrode acting as the active electrode. U.S. Pat. No.4,232,676 discloses pairs of electrodes in which the voltage applied maybe either direct current or alternating current but in either case thevoltage difference applied between all of the electrodes is the same.U.S. Pat. No. 4,706,667 discloses a pair of return electrodes flanking acutting electrode. U.S. Patent Application Publication No. 20030130658discloses multiple electrodes having dissimilar materials in which RFpower is applied to all of the electrodes.

The present inventors have recognized that applying a direct currentbetween the electrodes of a bipolar electrosurgical blade reduces orprevents the formation of short circuits, even when the electrodes inblades are close together. The present inventors have further recognizedthat the propensity for such short circuiting to occur can be reduced bylimiting the amount of exposed electrode surface area. The presentinventors have yet further recognized that such application of directcurrent between electrodes and limiting of electrode surface areas aremutually beneficial and complement each other.

When conventional bipolar blades are used, eschar tends to start to formon one electrode or another. The deposit then grows in thickness as itpropagates from that electrode, increasing the electrical impedance atthat electrode from what it would be absent the eschar deposit. As theeschar deposit grows it can span the gap between active and returnelectrodes in bipolar devices, leading to a short circuit current pathfor the RF power that reduces or prevents power transfer to tissue, thusinterfering with or preventing the desired surgical effect fromoccurring.

In short, the present inventors have recognized that a means is neededto prevent the formation or accumulation of the short circuits frommaterials formed by electrosurgical tissue decomposition processes. Thevarious embodiments comprise an electrosurgical instrument that includesa multiplicity of electrodes with at least one active and at least onereturn electrode. In a system context, the electrodes of theelectrosurgical instrument have not only alternating current flowing butalso direct current flowing between at least one active electrode or atleast one return electrode and another electrode. Such direct currentreduces or prevents the formation and accumulation of electrosurgicaltissue decomposition products on electrodes. The mechanisms by whichdirect current reduces or prevents eschar accumulation are not preciselyknown but are believed to include effects caused by electrolysis ofwater and shifts in chemical reactions. Electrodes having a morenegative voltage are believed to accumulate small amounts of hydrogen ina layer believed to restrict eschar accumulation. The negative charge isalso believed to inhibit dehydrogenation reactions that would otherwiseoccur at the temperatures that exist during electrosurgery, thusinhibiting the formation of at least some of the carbon-richconstituents that comprise eschar.

The method of reducing eschar on bipolar blade electrodes by applyingdirect current may be applied when other means are employed to reduceunnecessary/undesired electrical discharge during electrosurgicalprocedures. Such reduction(s) reduce the amount of direct currentrequired to reduce or prevent eschar accumulations and are achieved viaenhanced localization of electrical power transmission to a tissue site.More particularly, the various embodiments markedly reduce electricaldischarge from both functional and nonfunctional areas of anelectrosurgical instrument by insulating either or both functional andnonfunctional areas. The amount of direct current required to reduce orprevent eschar accumulation is reduced when one or more means areemployed to reduce the local heating that promotes eschar formation.Such means for reducing local heating include providing for an effectivelevel of heat removal away from functional portions of anelectrosurgical instrument and/or by otherwise enhancing the localizeddelivery of an electrosurgical signal to a tissue site such as byreducing the exposed areas of either or both functional andnonfunctional areas by using thermal insulation.

Various embodiments of the present invention comprise an electrosurgicalinstrument that includes a multiplicity of electrodes for carryingelectrosurgical power in which the electrodes are electrically isolatedfrom each other and provide for being connected to an ESU in an overallsystem such that at least one active electrode and at least one returnelectrode exist, thus forming at least one set of bipolar electrodes. Inan embodiment, direct current voltage may be applied across this pair ofelectrodes to reduce or prevent formation of electrosurgical tissuedecomposition products (ETDPs) such as eschar. The electrode with thenegative DC voltage will have little or no accumulation of ETDPs.However, the electrode with the positive DC voltage will tend toaccumulate ETDPs. Various embodiments include at least one electrode inthe system that is not directly connected to the RF power coming fromthe ESU. An electrode not powered by the ESU does not directly producethe predetermined surgical effect and any such electrodes are calledpassive electrodes herein. All passive electrodes are connected to onepole of a DC power source and the bipolar electrodes are connected tothe other pole of the DC power source. In use, the passive electrodeswould be connected to the positive pole and the bipolar electrodes wouldbe connected to the negative pole of the DC power source. Therefore,both of the bipolar electrodes are connected to RF power, which producesthe predetermined surgical effect and tends to produce ETDPs, and to aDC power source, while the passive electrodes are connected only to DC.In an embodiment system configuration, the negative DC on the bipolarelectrodes prevents or reduces accumulations of ETDPs and the absence ofRF power on the passive electrodes prevents or reduces accumulations ofETDPs on them.

In an embodiment of an electrosurgical instrument designed to makeincisions, there would be one pair of bipolar electrodes and one passiveelectrode. The regions near bipolar electrodes have temperatures thattend to promote eschar formation, but the negative DC current inhibitsor prevents eschar accumulation. The passive electrodes are not poweredby the ESU so the regions around them do not have the conditions thatpromote eschar formation.

In an electrosurgical instrument used to produce an electrosurgicaleffect on tissue in an environment where the electrodes are surroundedby a medium that provides electrical communication between at least oneof the bipolar electrodes and tissue, an example of such a medium beingan electrically conductive liquid containing substantial amounts ofwater, one or more pairs of bipolar electrodes may be employed, with orwithout the presence of one or more passive electrodes. In this secondinstance the bipolar electrodes of the system would have RF powerapplied to them that has a voltage bias that leads to a nonzero rootmean square (RMS) voltage that is adequate to electrolyze water local tothe electrodes. When one or more passive electrodes are used theconnections to DC power would be as previously described andelectrolysis would also occur. The electrolysis of water produces atleast a partial covering of gas bubbles around enough electrodes tocreate a sufficient impedance between the bipolar electrodes for an ESUto supply power adequate to produce the desired electrosurgical effect.

When one or more passive electrodes are used the bipolar electrodes areboth connected to the same pole of a DC power source. To prevent thiscommon connection from shorting the active and return electrodes one ormore electronic AC blocking components that allow DC current to flowwhile inhibiting passage of alternating current are put in series withthe connections from the DC power source to the bipolar electrodes. Inan embodiment, the components would be inductors sized to producesubstantial impedance, such as over about 500 ohms, to the RF powerproduced by the ESU while producing acceptably small DC resistance, suchas less than about 100 ohms. The direct current voltage differencebetween one or more passive electrodes and one or more of the bipolarelectrodes needs to be adequate to at least inhibit eschar accumulationwhile not producing too much electrolysis, such as by being at leastabout 0.5 volts and less than about 100 volts. Relatedly, insulatingmaterial may be interposed and interconnected between at least the twobipolar alternating current electrodes to define an electrosurgicalblade. Such electrical insulating material preferably has a dielectricwithstand strength of at least 50 volts and may comprise either a singlelayer or multiple layers with one or more other electrodes interposedbetween insulation layers.

In an embodiment, three electrodes that are substantially colinear overat least one dimension are used with at least part of the electrodesoriented parallel to each other with all of the electrodes separatedfrom and physically interconnected to the other electrodes by one ormore electrical insulating materials to define an electrosurgical blade.The electrosurgical blade may be configured so that at least part ofeach electrode may contact tissue or an electrically conductivesubstance in contact with tissue, with two of the electrodes beingbipolar electrodes with an alternative current voltage applied to themand the remaining electrode having a direct current voltage differencebetween it and the bipolar electrodes.

In various embodiments, an outer insulating layer made of one or morematerials selected to reduce thermal/electrical discharge fromnon-functional portions of the electrodes may be provided to surround atleast a portion of the bipolar electrodes, such as the active and returnelectrodes. In various embodiments, an outer insulating layer having athermal conductance of about 1.2 W/cm²° K and a dielectric withstandstrength of at least about 50 volts may be employed. Such insulatinglayer may advantageously comprise one or more materials with pores thathave been sealed with a sealing material so as to prevent biologicalmaterials from entering the pores. In an embodiment, such sealingmaterial may contain one or more of various silicate materials ormaterials that form silicates. In an embodiment, at least part of theouter insulating layer or the substance bonding at least one pair ofelectrodes comprise one or more materials that include a colloidalsilicate material and may further comprise one or more hydrolyzablematerials that in combination form a thermally insulative substance thatby itself is essentially hydrophobic and does not allow biologicmaterial to penetrate its surface.

In various embodiments, one or more of the electrodes are metal with theelectrodes provided to have a thermal conductivity of at least about0.35 W/cm ° K, and may advantageously comprise a metal selected from thegroup: gold, silver, aluminum, copper, tantalum, tungsten, columbium,and molybdenum, and alloys thereof. In various embodiments, one or moreof the electrodes may be coated or plated with a substance or elementthat imparts resistance to oxidation such as a plating of gold orsilver.

In various embodiments, the blade includes at least three conductivelayers or electrodes, including an intermediate layer or electrode thatdefines a peripheral edge portion of reduced cross-section (e.g., about0.001 inches thick or less) for electrosurgical power or direct currentpower transmission. Such intermediate layer or electrode may comprise ametal having a melting point of at least about 2600° F.

Heat sink structures may be included in various embodiments to establisha thermal gradient away from functional portions of the instrument(i.e., by removing heat from the electrodes). In an embodiment, the heatsink structures may comprise a phase change material that changes from afirst phase to a second phase upon absorption of thermal energy from theelectrodes.

In various embodiments, an electrosurgical blade is provided in whichthe electrodes are spaced apart using one or more types of electricallyinsulating particles, such as polymeric, glass, or ceramic beads, thathave maximum cross dimensions approximately equal to the distancedesired for spacing the electrodes from each other. In this regard, thespacing particles may be included as part of the above-noted electricalinsulating material provided between the electrodes. In turn, theparticles may be at least partially in contact with at least oneadditional material of the electrical insulating material that bonds tothe electrodes of the electrosurgical blade.

Various embodiments include a multielectrode electrosurgical instrumentand related system and method that employ structures for reducing orpreventing eschar accumulations on or between electrodes by a meansother than the spacing between electrodes, geometry of electrodes, orcomposition of electrodes. Such structures for reducing or preventingeschar accumulations on or between electrodes may require or beaugmented by electrode spacing, geometry, or composition. Variousembodiments apply to instruments in which at least one pair ofelectrically isolated electrodes are mechanically connected such thattheir spacing is limited to a predetermined range (such range possiblybeing a fixed distance) and electrically connected to an ESU such thatRF current will flow between the electrodes when they contact anelectrically conductive medium such as tissue or an electricallyconductive liquid or vapor. These electrodes are bipolar electrodes andany device having one or more sets of bipolar electrodes is a bipolarinstrument. All bipolar instruments, regardless of their intendedpurpose, design, shape, geometry, configuration, materials, or otheraspects are referred to as electrosurgical blades.

Various embodiments of the structures for reducing or preventing escharaccumulations on or between bipolar electrodes involve having directcurrent flow through at least one of the bipolar electrodes with atleast part of the current flow passing through tissue or passing throughat least one electrically conductive medium in electrical communicationwith at least one of the electrodes. In one embodiment the directcurrent flows between both of the electrodes of a pair bipolarelectrodes with at least part of the current flowing through tissue orpassing through at least one electrically conductive medium inelectrical communication with at least one of the electrodes. Someembodiments have at least one pair of bipolar electrodes and at leastone passive electrode (an electrode not powered by an ESU) and areconfigured and operated so direct current flows between said passiveelectrode and at least one of the bipolar electrodes with said directcurrent at least in part flowing through tissue or passing through atleast one electrically conductive medium in electrical communicationwith at least one of the electrodes.

Bipolar or passive electrodes may be any shape or shapes such as, butnot limited to, being substantially flat, having one or more curves,being shaped as closed curves such as rings or hoops, being shaped asnonclosed curves such as semicircles or crescents, being planar, beingnonplanar such as curved spatulas, having bends or curves such as hooks,encompassing volumes such as cups or cylindrical volumes, beingsubstantially blunt, having one or more regions that taper from onethickness to a lesser thickness, being solid such as spheres or balls,having opposing faces such as forceps or scissors, and having one ormore openings such as holes, meshes, pores, or coils.

FIG. 1 illustrates an embodiment in which a passive electrode is used.ESU 1 supplies power to multielectrode blade 2. Multielectrode blade 2consists of one or more active electrodes 3, one or more passiveelectrodes 4, one or more return electrodes 5, with the electrodesinsulated from each other by interior insulation 6. Recognize that ESU 1supplies alternating current power so that the flow of electric currentbetween active electrodes 3 and return electrodes 4 periodicallyreverses as the voltage output of ESU 1 changes. Multielectrode blade 2may be without insulation other than that separating the electrodes oradditional insulation may surround the electrodes. These aspects of theinvention are described later.

Active electrodes 3 may be one or more electrically conductive elementsand whenever referred to in the singular case are understood to alsoinclude the use of a multiplicity of electrodes connected electricallyto have substantially the same power source or power sources. Similarly,passive electrodes 4 may be one or more electrically conductive elementsand whenever referred to in the singular case are understood to alsoinclude the use of a multiplicity of electrodes connected electricallyto have substantially the same power source or power sources. Alsosimilarly, return electrodes 5 may be one or more electricallyconductive elements and whenever referred to in the singular case areunderstood to also include the use of a multiplicity of electrodesconnected electrically to have substantially the same power source orpower sources.

Power from ESU 1 to multielectrode blade 2 is conveyed via supplyconductive element 7, which can be an insulated metal conductor for atleast part of its length and terminates into handle 27 that holds themultielectrode blade 2 in a manner that conveys power to the activeelectrode 3 and that is convenient for having the multielectrode blade 2contact patient tissues. The electrical circuit for power from the ESU 1to the multielectrode blade 2 is completed via return conductive element8, which is can be an insulated metal conductor for at least part of itslength which terminates into the handle 27 that holds the multielectrodeblade 2 in a manner that conveys power from the return electrode 5 tothe return conductive element 8.

Passive electrode 4 is powered by the passive conductive element 9,which can be an insulated metal conductor for at least part of itslength that terminates into the handle 27 that holds the multielectrodeblade 2 in a manner that conveys power to the passive electrode 3.

DC power supply 10 supplies power to passive electrode 4 via passiveconductive element 9, preferably with the positive DC voltage beingsupplied to passive electrode 4. DC power supply 10 provides power toactive electrode 4 via DC conductive element 11. DC power supply 10provides power to return electrode 6 via DC conductive element 12.

One or more RF current impedance elements 13 and 14 may be in DCconductive elements 11 and 12 so that supply conductive element 7 andreturn conductive element 8 are kept substantially isolated from eachother and short circuit and to substantially isolate passive electrode 4and DC power supply 10 from being in RF current paths parallel to supplyconductive element 7 or return conductive element 8. RF currentimpedance elements 13 and 14 can be inductive elements providing atleast about 500 ohms impedance at the output frequency of ESU 1 andpreferably providing at least about 1000 ohms impedance at the outputfrequency of ESU 1 and more preferably providing at least about 5000ohms impedance at the output frequency of ESU 1. RF current impedanceelements 13 and 14 can be at least about 50 microhenries and preferablyat least about 1000 microhenries and still more preferably about 10,000microhenries. RF current impedance elements 13 and 14 need to convey DCpower and can be capable of carrying at least about 5 milliamperes,preferably at least 50 milliamperes and preferably have a DC resistanceof less than about 100 ohms and more preferably of less than about 50ohms and still more preferably less than about 20 ohms.

DC power supply 10 can provide voltage in the range of about 0.5 volt to100 volts, preferably in the range of about 2.5 volts to 50 volts andstill more preferably in the range of about 5 volts to 20 volts. DCpower supply 10 can provide current in the range of about 0.0100milliamperes to 1 ampere, and preferably in the range of about 10milliamperes to about 0.1 ampere.

ESU 1 is isolated from DC power by the presence of one or more DCblocking elements 15 and 16. DC blocking elements can be capacitorshaving a low equivalent series resistance (ESR) at the frequency of thepower from ESU 1 and having an impedance of less than about 500 ohms,preferably less than about 100 ohms and more preferably less than about50 ohms and still more preferably of less than about 10 ohms at theoutput frequency of ESU 1. In some embodiments, DC blocking element 15may be omitted and DC current flow blocked by DC blocking element 16.

Users can control when ESUs supply power by using either a footswitch ora switch in a handle that holds blades. When the switch is in the handleit is common for one or more signal wires to come from the ESU to thehandle and for the supply conductive element 7 to be part of the signalpath. As is known to those skilled in the art of ESU design, the RFpower supply and the signal path are isolated and separated in the ESUand commonly the control signal is a DC signal that uses the supplyconductive element 7. To not interfere with this control strategy the DCblocking element 15 can be located to prevent the control signal fromreaching ESU 1. FIG. 2 illustrates the same schematic as FIG. 1 with theaddition of control signal conductive element 17 and control switch 18.In an embodiment, control signal conductive element 17 and controlswitch 28 are in the handle 27, although they are not shown that way inFIG. 2. DC blocking element 15 can be placed so that it is not in serieswith control switch 28 and ESU 1. In an embodiment, DC blocking element15 is located in handle 27.

DC power supply 10 may take on any form that provides the proper voltageand current. In one embodiment it may be one or more batteries. Inanother embodiment it may be an external power supply powered from apower cord connected to AC line power from a wall outlet or power from aconnection in ESU 1. An embodiment obtains DC power from the RF powersupplied by ESU 1. In an embodiment, DC power supply 10 contains one ormore active components, such as diodes or other rectifying elements, andis connected to the RF output of ESU 1 and converts part of the RFoutput from ESU 1 into DC power.

FIG. 3 illustrates a bridge circuit that produces DC power from the RFpower supplied by ESU 1. DC power supply 10 contains four rectifyingelements, 17, 18, 19, and 20, configured in a bridge configuration. Avoltage control system 21 controls the output voltage. Voltage controlsystem 21 is illustrated as a capacitor but may consist of one or moreactive elements to further control voltage. The voltage control systemmay consist of a capacitor to reduce the magnitude of the voltagedeviations. In an embodiment, the voltage control system includes ameans for controlling the maximum output voltage, such as by using azener diode in series with a resistive load. One or more RF voltagereduction elements, 22 and 23, are used to drop the voltage output byESU 1 to produce a DC output voltage in the range desired. The presenceof one or more RF voltage reduction elements, 22 and 23, reduces thepower dissipation requirements that may be imposed on voltage controlsystem 21. Rectifying elements, 17, 18, 19, and 20 can be diodes and maybe of any type that has a reverse recovery time compatible withfrequencies of at least 20 kHz, preferably of at least 100 kHz and evenmore preferably of at least 200 kHz and still more preferably of atleast 500 kHz to be compatible with most of the ESUs being used, andfinally compatible with at least 2 MHz to be compatible with almost allESUs being used. Rectifying elements, 17, 18, 19, and 20 need towithstand the voltages output by the ESU and the RF voltage reductionelements, 22 and 23 allow the use of a range of diodes, such as Schottkydiodes, that can withstand preferably at least 500 volts and morepreferably at least 1000 volts.

In various embodiments, one or more of the elements of DC power supply10, RF current impedance elements 13 and 14, and DC blocking elements 15and 16 may be incorporated into the ESU 1, incorporated into an adapterthat connects to ESU 1, incorporated into plugs and connectors used toconnect supply conductive element 7 and return conductive element 8 toESU 1 (these plugs and connectors are not shown in FIGS. 1, 2, or 3), ormay be incorporated into the handle 27.

In use, connections are made to ESUs with a plug that connects supplyconductive element 7 to a power supply connector on the ESU and withanother plug that connects return conductive element 8 with a returnconnector on the ESU. In an embodiment, the elements of DC power supply10, RF current impedance elements 13 and 14, and at least one of the DCblocking elements 15 or 16 are housed in a plug that connects the supplyconductive element 7 to the ESU and that has a wire that passes from itto a plug that connects to a return connector on the ESU. In anotherembodiment, the elements of DC power supply 10, RF current impedanceelements 13 and 14, and at least one of the DC blocking elements 15 or16 are housed in the handle 27 which holds the blade. Such embodimentsmay either be reusable or may be a single use sterile disposable.

FIGS. 1, 2, and 3 illustrate the passive electrode being between theactive and return electrodes. This arrangement is not required. Passiveelectrodes may be anywhere that allows them to be in electricalcommunication with the active electrodes. Passive electrodes do not needto be mechanically connected to the device of which the active andpassive electrodes are a part. For example, one or more passiveelectrodes could attach to the patient in the form of one or moreelectrode pads and connect to DC power supply 10 using a wire. Thepassive electrodes can be mechanically connected to the device of whichthe active and passive electrodes are a part.

The electrodes may be any shape, size, or arrangement that leads to aconfiguration and composition suitable for a particular application. Forexample, an arthroscopic ablation instrument used in a submergedelectrically conductive liquid may be configured with multiple activeand return electrodes with suitable shapes, such as in the form oflinear or curved edges or pins, close together at the end of a shaft anda single passive electrode could be spaced back away from end of theshaft and be in the form of a ring around the shaft. All of theelectrodes would be surrounded by electrically conductive liquid and,thus, be in electrical communication with the liquid. In anotherarrangement, a split ring that forms a bipolar pair could have inlaid apassive electrode.

FIG. 4 illustrates an embodiment that uses fewer components than thoseillustrated in FIGS. 1-3. Direct current is supplied directly betweenactive electrode 3 and return electrode 5. No passive electrode is used.Any direct current power source may be used when direct current issupplied directly between the bipolar electrodes. An embodiment uses RFpower supplied by the ESU and one or more rectifying elements. FIG. 4illustrates using rectifying element 24 to produce a DC voltage.Contrary to common design practice for rectifiers such as diodes,rectifying element 24 can have a reverse recovery time less than theperiod of the AC power supplied. Preferably the reverse recovery time ofrectifying element 24 is between about 0.05 and 0.5 the period of the ACpower supplied and more preferably is between about 0.1 and 0.25 theperiod of the AC power supplied. Using such reverse recovery times leadsto substantial reverse current flow through the rectifying diode beforeit starts to inhibit backwards current flow. This slow response leads toa substantially lower direct current voltage being applied across activeelectrode 3 and return electrode 4 than would otherwise occur usingcommon design practice. Preferably, diodes rated as standard or fastrecovery may be used. Preferably, diodes with a voltage withstand of atleast 300 volts and more preferably at least 1000 volts may be used.

DC blocking element 15 can interfere with passage of control signalsthat may need to pass between one or more switches in handle 27 and ESU1. FIG. 5 illustrates an embodiment that does not include a DC blockingelement in the supply conductive element 7. Control signal conductiveelement 17 and control switch 28 are illustrated to show that controlswitch 28 can be located anywhere. In an embodiment, the control switch28 is located in handle 27.

In configurations without passive electrodes the electrodes may be anyshape, size, or arrangement that leads to an arrangement suitable for aparticular application. For example, an arthroscopic ablation instrumentused in a submerged electrically conductive liquid may be configuredwith multiple active and return electrodes with suitable shapes, such asin the form of linear or curved edges or pins, close together at the endof a shaft. All of the electrodes would be surrounded by electricallyconductive liquid and, thus, be in electrical communication with theliquid. In another arrangement, a split ring that forms a bipolar paircould have inlaid a passive electrode.

Alternatives to the illustrated embodiments exist. For example, theembodiments of FIGS. 4 or 5 would tend to keep eschar from accumulatingon active electrode 3 but not offer the same level of protection toreturn electrode 5. A passive electrode with a separate DC supply couldbe included that would cause DC current to pass between the passiveelectrode and the return electrode and reduce or prevent escharaccumulations on return electrode 5.

ESU 1 may have multiple RF supplies connected via a multiplicity ofsupply and return conductive elements to a multiplicity of active andreturn electrodes that are not electrically connected and thus operatingsubstantially independently of each other to provide multiple voltagewaveforms, possibly with phase angles, frequencies, and voltages thatdiffer from one another. DC power supply 10 may have multiple directcurrent power sources connected via a multiplicity of passive supplyconductive elements to a multiplicity of passive electrodes or to amultiplicity of active or return electrodes that are isolated from oneanother from DC current supply.

Passive electrodes need to be close enough to the bipolar electrodes toallow DC current to flow between the passive electrodes and the bipolarelectrodes. The passive electrodes may contact patient tissue within sixfeet of the bipolar electrodes. In some embodiments, the passiveelectrodes may contact patient tissue within six inches of the bipolarelectrodes. In some embodiments, the passive electrodes may contactpatient tissue within one inch of the bipolar electrodes. For manyblades, such as those embodiments used for incisions, the passiveelectrodes may be within about 0.5 inches of the bipolar electrodes, andin some embodiments within about 0.1 inches of the bipolar electrodes,and in other embodiments within 0.010 inches of the bipolar electrodes.The closer spacing between the passive electrodes and the bipolarelectrodes reduces the overall size of the instruments and reduces theamount of tissue through with which DC current passes.

FIG. 6 illustrates an electrosurgical instrument configuration withblade 29 connected to shaft 30. Shaft 30 typically connects to a handle(not shown) and typically provides means in the form of one or moreconductors for conveying electrical power to blade 29. The blade 29includes a functional portion, or contact face 26 (e.g. a cutting edge),for contacting patient tissue. FIGS. 7, 8, 9, and 11 are cross sectionsof blade 29 in FIG. 6 when viewed through cross section AA.

FIGS. 7, 8, 9, 10, and 11 illustrate various example embodimentconfigurations of multielectrode blades. To reduce DC current flowvarious embodiments limit the amount of exposed electrodes surface areaby extending interior insulation 6 over all of the interior surfaces ofthe electrodes except for the functional surfaces. To further reduce DCcurrent flow an embodiment employs outside insulation 25 to limit theelectrode surface area exposed on the outside of the blades. Theseconfigurations show passive electrode 4 between active electrode 3 andreturn electrode 5. As described earlier, this arrangement is notrequired. However, when this configuration embodiment is used,insulation between the nonfunctional surfaces of active electrodes 3 andreturn electrodes 5 can be included. If, for example, the activeelectrode is between the passive and return electrodes, the outersurface of the passive electrode does need to be insulated to reduce DCcurrent flow when only the functional areas of active and returnelectrodes already have limited surface areas exposed.

FIG. 7 illustrates a configuration in which the electrodes taper to fineedges and the blade is shaped to present a substantially flat contactface 26 where only the sharp edges of the electrodes are exposed throughthe surface of the interior insulation 6 and outside insulation 25. FIG.7 illustrates only one active electrode 3 and one return electrode 5,however multiple active and return electrodes could extend out in analternating arrangement. Such arrangements would increase the size ofthe flat contact face 26 through which the electrodes emerge. Thesemultiple electrode arrangements can be used for applications where largesurface areas are to undergo electrosurgical treatment, such as inarthroscopic tissue ablation procedures. For these applications anembodiment has the electrodes emerging from the surface to form a roughsurface that also mechanically abrades the surface of the tissue as itpenetrates the tissue. For these applications, the electrodes mayprotrude between about 0.0001 and about 0.5 inches, and in anembodiment, the electrodes protrude between about 0.001 and about 0.1inches. For such applications a single passive electrode can be used andin an embodiment, the passive electrode can be located away from theregion where the active and return electrodes are located to maximizethe amount of surgical effect caused by the active and return electrodein a give surface area. The passive electrode can be attached to theshaft of the instrument within about 0.5 inches of the location of theactive and return electrodes and no restriction exists regarding minimumspacing between the passive electrode on the shaft and active or returnelectrodes on the working surface where the surgical effects occur.

For making incisions it is preferable for the width of the bladecontacting tissue to be small to reduce drag. For making incisions it isfurther preferred to have small surface areas for functional areas andto also have small surface areas for nonfunctional areas near active andreturn electrodes to reduce the total exposed surface area whereelectrosurgical effects occur. Having small surface areas reduces thetime that tissue is exposed to conditions that cause ETDPs and alsoreduces the residence time of ETDPs in the hot regions near the activeand return electrodes. Long residence times tend to promote tissuedecomposition and the ensuing formation of smoke, eschar, and collateraltissue damage. The preferred small exposed surface areas whereelectrosurgical effects occur reduce the formation of smoke, eschar, andtissue damage. Various embodiments for blades used for incisions taper aportion of the blade by tapering at least the outside insulation 25, asshown in FIG. 7 such that the narrowest part of the blade is the contactface 26 where the functional areas are located, which is the same areaswhere active electrode 3 and return electrode 5 are exposed. FIG. 8illustrates an embodiment in which the electrodes 3, 4 and 5, andinsulation 6 and 25 are shaped to form a constantly curving strictlyconvex surface at the functional contact face 26. The strictly convexprofile reduces the residence time of material in regions where smoke,eschar, and tissue damage occurs. FIG. 8 also illustrates an embodimentin which electrodes are shaped to further taper the blade in order toreduce residence time. The strictly convex shape in the functionalregions where the electrodes are exposed can be achieved without shapingthe blades to accentuate the taper.

In various embodiments, the tapered blade portion where the blade taperstoward the contact face 26 can be concave while keeping the contact face26 where the electrodes are exposed strictly convex. FIG. 11 illustratesan embodiment that has a concave surface where the blade tapers and isconvex where the electrodes are exposed. The strictly convex contactface 26 can be used where the electrodes contact the tissue and betweenthe electrodes. The portions of the blades outside of the electrodes canbe tapered so that they are either flat or concave, as illustrated inFIG. 11.

For blades used for making incisions it is preferable for the blades tobe thinner than about 0.5 inches and more preferable for them to bethinner than about 0.05 inches. When blades are too thick they impedethe incision process and drag through the tissue. Metal electrodespreferably thinner than about 0.2 inches and more preferably thinnerthan about 0.1 inches and still more preferably thinner than about 0.02inches should be used to produce blades with the desired thinness.Insulation thickness on the outside of the bipolar electrodes and thetotal insulation thickness between bipolar electrodes preferably thinnerthan about 0.2 inches and more preferably thinner than about 0.1 inchesand still more preferably thinner than that about 0.02 inches should beused to produce blades with the desired thinness. The spacing betweenelectrodes can be between about 0.001 and 0.2 inches, preferably betweenabout 0.002 and 0.100 inches and more preferably between about 0.005 and0.015 inches.

FIG. 9 and FIG. 10 illustrate a blade in which slightly more electrodemetal than the very edge is exposed through the insulation. FIG. 10illustrates an elongated blade in which the active electrode 3, passiveelectrode 4, and return electrode 5 extend along a dimension to formapproximately coplanar surfaces and, consequently, has a contact face 26in the form of a cutting edge that is substantially longer than it iswide. Such configurations may be suitable for blades used to makeincisions. Illustrated is a configuration in which the cutting edge ofcontact face 26 is approximately a straight line. The cutting edge couldhave other shapes, for example having one or more parts that have shapesthat approximate part of an ellipse or circle instead of approximately astraight line.

If part of the edge is behind or covered by insulation thenelectrosurgical energy transfer is inhibited and accomplishing thecorresponding desired predetermined electrosurgical effect is hindered.To provide reasonable manufacturing tolerance and not have part of theedges of electrodes exposed more than an extremely fine edge needs to beexposed. More than 90 percent of the active and return electrode edgesalong the functional surfaces can be exposed, preferably more than 95percent of the active and return electrode edges be exposed along thefunctional surfaces, and more preferably that more than 99 percent ofthe active and return electrode edges be exposed along the functionalsurfaces. Furthermore, it is preferable to limit the DC current flow andresidence time of tissues at the conditions that cause smoke, eschar,and tissue damage. The smallest dimensions (the widths) of the edges ofthe active and return electrodes can be smaller than about 0.020 inches,preferably that the widths of the edges of the active and returnelectrodes are smaller than about 0.005 inches and more preferable thatthe widths of the edges of the active and return electrodes are smallerthan about 0.001 inches and still more preferable that the widths of theedges of the active and return electrodes are between about 0.00001 and0.001 inches.

FIG. 11 illustrates the active electrode 3, passive electrode 4, andreturn electrode 5 emerging from the insulation of a blade. Thisarrangement in which electrodes have at least one region exposed withoutinsulation can be employed in various embodiments for either connectingblades to handles or to have blades connect to other features, such asshafts, that will become part of a final device. The exposed regions ofthe electrodes can vary and the lengths of the blades can be stepped orotherwise made unique to facilitate producing electrical contactsurfaces.

From an overall system standpoint, the DC power source could be part ofthe ESU or may be external to the ESU. When external to the ESU the DCpower source could be an adapter connected to the ESU to which asurgical instrument is connected or the DC power source could be a partof the surgical instrument. The DC power source could be self contained,such as a battery, could obtain power from an outside source, such as anAC wall outlet, or it could obtain its power from the RF power suppliedto the instrument by the ESU. When obtaining power from the RF powersupplied by the ESU one or more rectifying components such as diodeswould be used. Typically one or more electronic components, such ascapacitors, would be used to isolate the ESU from the DC power beingadded to the RF power supplied to the instrument while still allowing RFpower to be conveyed to the instrument.

Which electrodes are active, return, and passive may be fixed andunchanging or the polarities of the electrodes may change during use.Changing polarities during use may facilitate procedures such as makingincisions by reducing the amount of force required to move a bladethrough tissue. Switches would be used to change the connections of theelectrodes to active, return, and DC power poles. Typically, suchswitches would use one or more electronic semiconductor components suchas bipolar transistors, field effect transistors, or insulated gatebipolar transistors. The switching can be facilitated by timing thetransition from one polarity setting to another during those times whenthe RF voltage applied to the blade is substantially less than the peakvoltages applied by the ESU. Such low voltage switching would includeswitching during the times when voltages are close to zero, such ascommonly occur with ESU outputs having crest factors greater than about1.5, and commonly are greater than 2 or when ESU outputs have dutycycles less than 100% and commonly less than 75 percent.

Closely spaced electrodes may be made by placing a thin coat of aninsulating material that bonds to electrode material on an individualelectrode element and then placing another electrode element on theinsulating bonding material. The bonding material needs to produce asurface with dielectric strength suitable for withstanding the voltagedifference across the electrodes. Suitable materials includepolydiorganosiloxanes, silicone elastomers, fluorosilicones, andpolytetrafluoroethylenes. Other approaches include laminating a solidpolymer sheet between electrode elements and interposing layers ofadhesive. Additional approaches include using ceramic material thatbonds the electrodes, including formulating the ceramic with particlesor fibers with dimensions that space the electrodes apart to facilitatemaintaining desired electrode spacing and planarity. An embodiment usesa ceramic material to bond the electrodes such that the bonding materialextends between the electrodes to the exposed surfaces of theelectrodes. An acceptable ceramic material to use for bonding is one ofthe outer insulating materials described below. Another embodiment usesone of the insulating materials described below that includes one ormore hydrolyzable silanes including those that have halogens and evenmore preferable is to use one of the insulating materials describedbelow that contain one or more hydrolyzable silanes that containfluorine. In another embodiment, high temperature polymer materials maybe used to bond the electrodes.

In an embodiment, the bonding material used between electrodes may haveadded to it particles that are not electrically conductive that willspace the electrodes apart when the electrodes are pressed together orotherwise fixtured during manufacturing. Examples of such particles areglass beads or fibers, ceramic beads or fibers, or polymeric beads orfibers. Such particles can be generally rigid and capable ofwithstanding temperatures greater than about 200° F. without deformingunder load, such as glass or ceramic beads or fibers. Also, such spacingparticles individually have approximately uniform dimensions such asbeing spherical. The spacing particles can comprise a range ofdimensions, but in general the largest size particles will be the onesthat hold the electrodes apart when they are pressed together orotherwise fixtured. The maximum diameter of the largest particles, orequivalent dimension that determines the spacing of the electrodes, canbe between about 0.001 and about 0.2 inches, more preferably betweenabout 0.002 and 0.100 inches and even more preferably between about0.005 and about 0.015 inches.

The amount of electrosurgical products produced depends upon the amountof energy applied to tissue, the rate at which the energy is applied,and the length of time that tissue is exposed to sources of the energy.While conventional electrosurgical systems have attempted to controlthese factors by means of ESU settings, the present inventors haverecognized that the configuration of electrosurgical blades also affectthe time and amount of energy applied to portions of tissue, and thus tothe generation of electrosurgical products. For example rough bladefunctional surfaces tend to retain tissue fragments and thus expose suchtissue fragments to electrosurgical energy for longer durations thanoccurs when the blade has smooth functional surfaces. If recesses orpockets exist where material can be held in place in close proximity tothe functional surfaces, the residence time for chemical reactions tooccur increases for trapped materials. With increased residence time,more lysis occurs, leading to increased smoke and eschar production. Aslow molecular weight materials are lysed from trapped materials theyleave as smoke and gases that are relatively rich in hydrogen, leavingbehind an increasingly carbon-rich material. This material is eschar.When deposited on the surface of an insulating layer it effectivelywidens the electrically conductive edge, which exposes more tissue toelectrosurgical energy and increases the time at which tissue is exposedto lysing conditions. Exposing more tissue to lysing conditions andexposing tissue for longer periods to such conditions causes more smokeand eschar to form, and thus it is desirable to prevent or reduce theoccurrence of such conditions.

Using cutting as an example electrosurgical process, the power settingstypically used during electrosurgery employing conventionalelectrosurgical systems are over 30 Watts, and often are on the order of40 to 100 Watts. Theoretically, the amount of power required for cuttingis much lower, between about 2 and about 15 Watts. The surplus powerbeyond that theoretically required drives unwanted reactions such as theproduction of smoke and eschar as well as overheating tissue that killscells.

The various embodiments employ blade geometry, blade composition or acombination of blade geometry and composition to reduce or prevent smokeproduction, eschar accumulations, or tissue damage. The embodimentsfocus electrosurgical energy to a small amount of tissue for a shortduration compared to the amount of tissue and duration than is customaryduring electrosurgery using conventional technology. In the embodiments,the electrosurgical energy flows from a conductive elements that issurrounded by insulation except for an exposed edge or point. Providinga relatively small exposed edge or point on the conductive elementsrestricts RF energy flow to this portion of the conductive element,minimizing energy transfer from the rest of the conductive elementswhich is covered by insulation. In some embodiments, the exposed edge onthe conductive elements can be formed by tapering down the insulationcovering from its thickness at the wide part of the conductive elementto minimal thickness adjacent to the exposed edge, as illustrated inFIGS. 15 and 16. In other embodiments, the conductive elements geometryends in a point that is not covered by insulation, as also illustratedin FIGS. 15 and 16.

Various embodiments comprise electrosurgical instruments that use bladeshape and composition to reduce the production of smoke and eschar by,among other methods, reducing the time that materials are exposed toelectrosurgical energy. The result is reduced smoke production, reducedeschar production, and reduced tissue damage.

Various embodiments include electrosurgical instrument features thatpromotes the free flow of electrosurgical decomposition products such assteam, gases, and vapors away from regions near the functional surfaceswhere electrosurgical energy interacts with tissue and such gaseousdecomposition products form It is believed that facilitating the flow ofgaseous decomposition products away from the functional surfaces wherethey are generated reduces the local gas pressure in the vicinity of thefunctional surfaces which would otherwise rise with the buildup ofgaseous products. By reducing the pressure and promoting the flow ofelectrosurgical decomposition products, the conditions which causepyrolysis and electropyrolysis of tissue and electrosurgical productsare reduced, particularly in the vicinity of the functional surface justremoved from where the desired electrosurgical effect occurs. It isbelieved that continued pyrolysis and electropyrolysis ofelectrosurgical decomposition products leads to more generation of smokeand eschar. Thus, by reducing pressure, and thus temperatures, in thevicinity of the functional surfaces and facilitating the escape ofelectrosurgical decomposition products, generation of smoke and escharcan be substantially reduced.

In various embodiments, the electrosurgical instrument or blade featuresa narrow surface, edge or point in the vicinity of the functional areathat reduces the length of the path that gases or vapors must traversefrom the point of generation to reach ambient conditions, thus thedistance and time during which decomposition products are exposed tohigh temperatures. In such embodiments, examples of which areillustrated in FIGS. 15-20, the functional surface is an edge of theblade that has at least one dimension (such as thickness) which is lessthan the corresponding dimension (such as thickness) of nonfunctionalsurfaces. In various embodiments, the edge or point is comprised of ametal conductor that is surrounded by insulation except for a sectionwhere the metal is exposed. In such embodiments, the outer profile ofthe insulation where the metal conductor is exposed is thinner than theouter profile at a distance removed from the exposed surface. In anembodiment, the edge or point is shaped so that it forms an acute anglewhere it comes in close contact with tissue during use. This aspect ofthe embodiments reduces the local gas pressure compared to, for example,a blade that has a relatively flat surface shape adjacent to thefunctional surface, such as when the combination of the insulation andconductive elements form a round or parabolic profile, such asillustrated in FIGS. 12 and 13. In some embodiments, the edge is formedby tapering the profile so that the radial dimension at the functionalsurface is less than the radius of part of the nonfunctional surface ofthe blade.

In other embodiments, the shape of the blade is configured such thatwhen it contacts tissue and is moved through tissue, the amount of timethat a tissue surface is adjacent to the functional surface is reducedor minimized. In some embodiments, the shape of the blade is configuredsuch that it substantially has only a single line or point of contact ofthe functional surface with tissue. Such embodiments differ fromconventional electrosurgical blades which typically allowelectrosurgical energy to flow into tissue from both the edge and thesides of the blade. Some embodiments, an example of which is illustratedin FIG. 24, also differ from conventional blades that have two edgesthat are substantially not collinear, such as come to a form a 120degree angle as illustrated in FIG. 21, such that one of the edges couldbe held approximately parallel to the tissue during use. Conventionalblades of this configuration allow the same section of tissue to beexposed to electrosurgical energy over the entire time that the parallelsection contacts the section of tissue, as illustrated in FIG. 22.

In various embodiments, the electrodes have functional surfaces in whichthe conductive elements are strictly convex in shape and thus do notcontain recesses. Strictly convex surfaces do not have recesses in whichtissue or electrosurgical decomposition products may become trapped. Iftissue or electrosurgical decomposition products becomes momentarilytrapped in a recess, such materials are exposed to electrosurgicalenergy and high temperature for a longer time, leading to generation ofsmoke and eschar. Such embodiments differ from conventional blades whichhave a nonconvex surface of the outer insulating surface where itextends to the edge of a metal electrode leaving the electrode slightlyrecessed into the insulation.

In various embodiments, one or more of the electrodes are metal with theelectrodes having a thermal conductivity of at least about 0.35 W/cm °K. Such electrode metals may comprise a metal selected from the group:gold, silver, aluminum, copper, tantalum, tungsten, columbium, andmolybdenum, and alloys thereof. In various embodiments, one or more ofthe electrodes may be coated or plated with a substance or element thatimparts resistance to oxidation, such as a plating of gold or silver.

In various embodiments, the insulation is selected and fabricated so ithas a surface free energy that reduces the propensity forelectrosurgical decomposition products to stick to the surface. In someembodiments, at least the edge of the conductive elements is composed ofa material that reduces the propensity for electrosurgical decompositionproducts to stick to the surface and that is configured with a geometrythat promotes the flow of thermal energy away from the edge whenelectrosurgical energy is being applied to tissue.

In the various embodiments, at least one electrically conductiveelements is electrically connected to an ESU. When connected to an ESU,RF current will flow from the electrically conductive elements whencontacting or in close proximity with an electrically conductive mediumsuch as tissue or an electrically conductive liquid or vapor.

The various embodiments described generally above maybe understood byreference to the example embodiments illustrated in the figures, whichwill now be described in more detail.

Referring to FIG. 12, an electrically conductive element 31, which istypically metallic, can be surrounded by insulation 32. The conductiveelement 31 may be of any number of shapes, such as, but not limited to:substantially flat; having one or more curves; shaped as closed curves,such as rings or hoops; shaped as nonclosed curves, such as semicirclesor crescents; planar; nonplanar, such as curved spatulas; having bendsor curves, such as hooks; encompassing volumes, such as cups orcylindrical volumes; substantially blunt; having one or more regionsthat taper from one thickness to a lesser thickness; having opposingfaces, such as forceps or scissors; and having one or more openings,such as holes, meshes, pores, or coils.

The conductive element or electrode 31 can have a tapered section 33.Additionally, the insulation 32 can have a tapered section 34. Thecombination of tapers on the conductive element 31 and the insulation 32can produce bevels that transition down to the conductor edge 35 of eachelectrode in the blade or at least the active and return electrodes.This leaves the conductor edge 35 exposed (i.e., not covered byinsulation) so that electrical energy can transfer to tissue from theedge via conduction or capacitive electrical coupling, or bothconduction and capacitive coupling, including with or without otherenergy transfer mechanisms that may be facilitated by an exposed edgeincluding energy conveyed by conduction or radiation or a combination ofconduction and radiation. The conductive element tapered section 33provides a cross sectional profile that reduces the width of theconductive element 31 to form the conductor edge 35 for that electrode.The tapered section 33 may be reduced on one side of the profile orboth, and may take on a variety of shapes as the width is reduced. Forexample, the cross sectional profile of the conductive element mayinclude a radius of curvature that produces a concave profile, asillustrated in FIG. 12. As another example, the cross sectional profileof the conductive element may have a predominately flat profile, asillustrated in FIG. 16. In a further example embodiment, the crosssectional profile may have multiple radii of curvatures producing across sectional profile which combines concave and convex sections. In afurther example embodiment, the cross sectional profile of the outer twoelectrodes (i.e., the active and return electrodes) in a three electrodeblade embodiment may include a radius of curvature that produces aconcave profile on the exterior sides. Alternatively, the exteriorsurface may simply have a linear profile, as illustrated in FIGS. 25A-C.In a further example embodiment, the center passive electrode in a threeelectrode blade embodiment may include a linear or concave taper shapeon both sides allowing the two exterior electrodes (i.e., the active andreturn electrodes) to be angled inward toward the blade centerline toprovide a narrow tip section as illustrated in FIG. 25C.

Referring to FIG. 12, the conductor edge 35 is the portion of theconductive element 31 exposed from the insulation 32. In someembodiments, the conductor edge 5 is positioned at the edge of theblade. The conductor edge 35 is intended to be used in close proximityor touching tissue 36, as illustrated in FIG. 12. A narrow gap region 37between the conductor edge 35 and tissue 36 is where electrosurgicalenergy interacts with tissue 36 via the transmission of electrosurgicalenergy.

In the blade configuration shown in FIG. 12, the outer profile of thetip end of the blade is approximately parabolic. As a result, in thevicinity of the conductor edge 35, the outer profile defined by theinsulation 32 is relatively wide compared to the thickness of theconductor edge 35. This aspect of the blade is shown in more detail inFIG. 13.

FIG. 13 is a magnified view of the area around the narrow gap region 37illustrated in FIG. 12. Shown are electrical conductive element 31,outer insulation 32, conductor edge 35, and tissue 36. Sparks and othermeans of electrosurgical energy transfer occur mostly in the primaryreaction region 48, producing electrosurgical decomposition productswhich are depicted by the dashed arrows 39. The electrosurgicaldecomposition products 39 include gases, such as steam, entrainedparticles, and liquids that have been heated. The volume ofelectrosurgical decomposition products 39, particularly the gases, willincrease local gas pressure in the region 48 that force theelectrosurgical products out through the gap 37 formed between thetissue 36 and the combination of the blade insulation 32 and conductoredge 35. For clarity, only one conductor is shown in FIGS. 12 and 13,whereas in various embodiments multiple electrodes may be present.

The flow of the electrosurgical decomposition products 39 away from thefunctional area may be inhibited by the viscous drag that results fromthe narrowness and length of the gap 37 as well as the tortuousity ofthe path due to the roughness of the tissue, roughness of the blade, andcontact between the tissue 36 and the insulation 32 or conductor edge35. The more the flow of electrosurgical decomposition products 39 isinhibited, the greater the local pressure rise and the longer thereaction products remain exposed to high temperatures in the region 48.In use, tissue 36 which contacts the insulation 32 in the primaryreaction region 48 may form temporary sealed pockets of gas, furtherinhibiting flow of reaction products. The inhibited flow from eitherviscous drag or temporarily sealed pockets is exacerbated when the bladeis pressed into the tissue 36 by the user as a natural part of thesurgical incision process. The result of these overall interactions isthat the electrosurgical decomposition products in the gap region 48between the tissue 36 and the insulation 32 and conductor edge 35becomes pressurized to sufficient pressure to expel reaction products toachieve an approximate and temporary equilibrium between the rate ofmaterial forming and the rate of material leaving the region 48.

Even when the local pressure is high enough to force electrosurgicalproducts from the primary reaction region 48, the resulting localtemperature can be high enough to promote rapid pyrolysis and causeelectropyrolysis to occur. A major constituent of many tissues is water.The conversion of water to steam is a significant absorber of energywhen electrosurgical energy interacts with tissue. As a firstapproximation, the equilibrium temperature of saturated water and steamat the local pressure within the reactive region 48 can be used toestimate the minimum temperature that tissue in this region is exposedto during electrosurgery. For example, the estimated range of forcesapplied to blades by a user during an incision of tissue is about 0.15N/mm to about 0.625 N/mm, where N/mm is Newtons per millimeter of blademovement through the tissue. If a blade has a blunt (approximately flat)profile facing the tissue (as is the case with the broad parabolicprofile illustrated in FIG. 13) with a width of about 0.0508 mm (0.002inches), then the pressure applied to the tissue when the applied forceis 0.2 N/mm will be approximately 3.94 N/mm (3.94 MPA). At this pressurewater boils to steam at about 250° C. (482° F.), a temperature that ishigh enough for tissue to pyrolyze and leave carbon-rich residues.Carbon-rich residues are those in which at least some of theelectrosurgical decomposition products have a ratio of hydrogen atoms tocarbon atoms less than about 1. Such carbon-rich residues are believedto be a major constituent of eschar.

The wider the contact surface in the primary reaction region 48, thegreater the likelihood that tissue 36 will contact and momentarily stickto insulation 32 and the conductor edge 35, and thus, the greater thelikelihood that materials will be sealed briefly in fixed volumes (e.g.,pockets). As electrosurgical energy flows into a sealed volume withinthe reaction region 48, the equilibrium temperature will increase aspressure increases until the pressure reaches a point sufficiently highto burst through the seal of tissue stuck to the blade. Therefore, widecontact surfaces tend to lead to localized high pressure and hightemperature regions as well as increase the time that electrosurgicaldecomposition products reside within the vicinity of the primaryreaction region 48. Various embodiments use blade geometries thatprevent local temperatures proximate to the conductor edge 35 fromexceeding about 190° C. based upon saturated steam conditions andassuming an applied usage pressure of 0.2 N/mm. Some embodiments useblade geometries that limit the pressure on the edge of the blade toless than about 1.2 MPa.

Referring to FIG. 14, some embodiments use blade geometries whichinclude an edge depth 62 of about 0.254 mm (0.010 inches) with a bladeedge half width 61 of less than about 0.5 mm (0.02 inches). In a furtherembodiment, the blade edge half width 61 is less than about 0.25 mm(˜0.01 inches), and in yet another embodiment the blade edge half width61 is less than about 0.12 mm (˜0.005 inches).

To achieve reaction conditions that lead to reduced smoke and eschar,blade profiles can be used that are generally tapered in the vicinity ofthe edge conductor such that a tangent to the insulation at theconductor edge forms an acute angle 38 (i.e., less than 90 degrees) withthe centerline of the blade as shown in FIGS. 17 and 19. Blade profileswith an acute insulation angle 38 are preferred over profiles that areof an approximately parabolic form as shown in FIG. 12. FIG. 15 and FIG.16 illustrate geometries where the outer blade profile defined byinsulation 32 is shaped with more than a single smooth curve and thatjoin at the conductor edge 35.

FIG. 15 illustrates an embodiment where the conductive element 31 issurrounded by insulation 32 and the conductive element 31 has a concavetaper 33 that results in a narrow conductor edge 35. In the embodimentillustrated in FIG. 15, the insulation 32 covering the conductiveelement 31 reduces in thickness toward the narrow edge until theconductive element metal is exposed forming the conductor edge 35. Inthis embodiment, the insulation 32 has an insulation taper 4 that alsohas a generally concave shape defined by the curves that smoothlyterminate at the conductor edge 35. This geometry presents fewopportunities for tissue to press against the edge of the blade to formseals or tortuous paths compared with the blade profile shown in FIG.12.

FIG. 16 illustrates an embodiment similar to that shown in FIG. 15except that the conductive element taper 33 and insulation taper 34 areapproximately linear (i.e., flat) instead of being concave. As with theembodiment shown in FIG. 15, the geometry of the embodiment shown inFIG. 16 provides little opportunity for tissue to press against the edgeof the blade and form seals or tortuous paths compared to the bladegeometry shown in FIG. 12. Other embodiments include an insulation taperformed such that the surface of the insulation follows more than onecurve defining the insulation taper in the vicinity of the conductoredge 35.

FIG. 17 illustrates a blade embodiment that includes an acute insulationangle 38. The insulation angle is the angle formed between a linetangent to the insulation bevel 34 at or near the conductor edge 35 anda line parallel to the centerline of the blade. FIG. 18 illustrates theinsulation angle 8 that occurs when the insulation taper 34 is becharacterized by a single continuous smooth curve (a broad parabola inthis case) compared to FIG. 17 where the insulation angle 38 that occursis characterized by two curves (flat lines in this case) thatessentially intersect at the conductor edge 35. FIG. 19 illustrates thecase where the insulation 32 transitions from one curve to anotherbefore two separate curves intersect near the conductor tip 35 formingan acute insulation angle 38.

In the various embodiments, the insulation angle 38 should be less than90 degrees, and preferably should be less than about 60 degrees, morepreferably less than about 50 degrees, and still more preferably lessthan about 45 degrees.

A number of geometries for the taper portion can be employed to achievean insulation angle of less than 90 degrees. FIG. 14 illustrates anarrow parabola geometry with an acute insulation angle. FIG. 15illustrates a concave geometry which results in an acute insulationangle. FIGS. 16 and 17 illustrate a flat (i.e., linear) taper with anacute insulation angle. FIG. 19 illustrates a two-curve geometryresulting in an acute insulation angle. FIG. 20 illustrates a bladecross-section that has an insulation taper 34 that is concave. FIG. 20also illustrates a conductive element 31 with a concave tapered region33 that reduces down to form the conductor edge 35. Embodiments withconductive elements that have substantially concave tapers down to theedge facilitate the production of an outer insulation profile that isalso concave as FIG. 20 illustrates.

The blade thickness profile embodiments illustrated in FIGS. 12-20 canbe used for a cutting blade with a planar shape similar to a scalpel, inwhich case the width of the blade would extend out of the page.

Restricting the amount of time that tissue and electrosurgicaldecomposition products are exposed to electrosurgical energy reduces theamount of eschar and smoke produced and reduces the amount of tissuedamage. When the edge of blade contacts tissue for a period of timelonger than is necessary to achieve the predetermined surgical effect,such as cutting, then more smoke and eschar are produced and more tissuedamage occurs. The various embodiments include insulation 32 over theconductive element 31 which insulates the outside of the blade exceptfor the exposed conductor edge 35, as has been illustrated in FIGS.12-20. The insulation 32 restricts the flow of electrosurgical energyfrom the conductive element 31 to the tissue 36 except at the conductoredge 35. To serve this function, the insulation 32 needs to be of anadequate dimension so as to restrict or prevent the flow electrosurgicalenergy. However, too much insulation may make the blade width excessive.

The conductive element 31 both conveys electrical energy to theconductor edge 35 and conducts thermal energy away from the conductoredge 35 to help keep the blade relatively cool. Making the conductoredge 35 thick would facilitate conducting heat away from the edge, butif the edge is too thick then more sealing of tissue against the edgecan occur with the coincident increase in smoke and eschar productionand tissue damage. The ability of the conductive element 31 to removethermal energy from the conductor edge 35 depends on the thermalconductivity of the material from which it is made. This relationshipbetween thermal conductivity and the width of the edge can be expressedas the product of thermal conductivity and the width of the conductoredge 35, such that a poorer thermal conductor needs a wider path than abetter thermal conductor. As used herein, the term “thermal pathconductance” refers to the product of the conductive element material'sthermal conductivity and the width of the thermal flow path, where thethermal conductivity is measured in W/m/° K at about 300° K and thewidth is measured in meters, leading to the units of thermal pathconductance being W/° K. The various embodiments can have a thermal pathconductance at the conductor edge of at least 0.0002 W/° K, preferablyof at least 0.0003 W/° K, more preferably of at least 0.0006 W/° K, andstill more preferably of at least 0.001 W/° K. For example, if thethermal path width is 0.0005 inches (1.27E-5 m) and the material used ismolybdenum having a thermal conductivity of about 138 W/m/° K, then thethermal path conductance is about 0.00175 W/° K. In a blade having aplanar configuration like a scalpel, the width of the thermal path willbe the thickness of the blade at the edge.

To reduce the amount of tissue heated, the electrosurgical energy isfocused in the various embodiments. One method of focusing the energy isto insulate the blade except for an exposed edge. Preferably, theexposed conductor edge 35 of the conductive element 31 is flush with theinsulation layer 32 so as to avoid any recessed pockets and anunnecessarily broad reaction area such as formed if the electrode isrecessed into a pocket in the insulation, the edge is coated with aninsulator, or the edge is rounded. In some embodiments, the conductoredge 35 adjoins the insulating layer 32 to form a singular taperedexterior surface. Focusing electrosurgical energy is further facilitatedby having a narrow conductor edge 35.

A flush, non-recessed conductor edge 35 further facilitates theelectrosurgical process beyond the focus of electrosurgical energy. Ifthe conductor edge is recessed within the insulation, then a pocketexists where tissue or electrosurgical decomposition products canaccumulate and remain exposed for long durations to electrosurgicalenergy, thus promoting continued pyrolysis and electropyrolysis. In anembodiment, no pockets or recesses exist where tissue or electrosurgicaldecomposition products can accumulate. Therefore, gaps or recessesbetween the conductor edge and the insulation are avoided in variousembodiments. By adjoining the conductor edge with the insulating layerto form a flush exterior tapered surface with no gaps or recesses, thesingular exterior tapered surface can take on a strictly convex shapeimmediately adjacent to the conductor edge. This embodiment reduces oreliminates opportunities for trapping tissue during use. Away from theconductor edge the profile of the insulation taper can be concave. Thisembodiment reduces residency time at high temperatures and reducespressure which reduces the equilibrium steam temperature.

In addition to avoiding gaps or recess between the conductor edge 35 andthe insulation layer 32, the conductor edge 35 itself should not haverecesses in the conductive element material that might promote thetrapping of tissue or electrosurgical decomposition products. Preferablythe conductor edge 35 is relatively smooth and does not have recessesalong its length or width, such sawtooth, gaps, pockets or holes thatare larger than about 32 microinches.

Embodiments of the invention include conductor edge shapes that arepointed, terminate to an acute angle, or are flat. Preferably, the shapeof the conductor edge 35 is not rounded. Preferably the conductor edgehas a thickness less than about 0.005 inches, more preferably less thanabout 0.002 inches, more preferably less than about 0.001 inches, andeven more preferably about 0.0005 inches or less.

The thickness of the insulation layer, particularly at the areaproximate to the conductor edge, affects the overall thickness of theedge of the blade. Enough insulation needs to be present to restrict therate of energy transfer out the sides of the blade into tissue orelectrosurgical decomposition products to prevent or reduce continuedchanges in those materials. Restricting the rate of energy transfer outthe sides is particularly important near the conductor edge wheretemperatures will be highest. If the insulation is thicker thannecessary to prevent continued changes in tissue or electrosurgicaldecomposition products, then the blade will be wider than necessary nearthe conductor edge, which increases the opportunities for sealing tissueagainst the conductor edge or the insulation near the conductor edge.

When conductive element 31 is tapered so that it is thinnest at theconductor edge 35, as illustrated in FIGS. 12-20, the temperature of theconductive element will decrease as the distance from the conductor edge35 increases. Therefore, the thickest insulation needs to be near theconductor edge 35, allowing the shape of the insulation 32 to have atapered region 4 that needs to be no thicker than it is near theconductor edge 35. The thickness of the insulation at the conductor edgecan be at least one half of the thickness of the conductor edge and morepreferably at least equal to about the thickness of the conductor edge.For example, if the conductor edge has a thickness of 0.001 inches thenthe insulation surrounding the conductor edge can have a thickness ofabout 0.0005 inches and preferably has a thickness of about 0.001inches.

The main portion of the conductive element 31 should be thick enough toreadily conduct heat away from the conductor edge 35. The width of theconductive element 31 can have a thickness before the taper portion 33that is at least about 5 times as thick as the conductor edge 35,preferably at least about 10 times as thick as the conductor edge 35,and more preferably at least about 20 times as thick as the conductoredge 35. For example, if the conductor edge is 0.001 inches thick andthe conductive element thickness before the taper begins is 0.020inches, then the ratio of the thickness of the conductive element to thethickness of the conductor edge 35 is 20.

In addition to the edge geometry, the overall configuration of the bladecontributes the generation of excessive decomposition products andincreased tissue damage. For example, FIG. 21 illustrates a bladeconnected to shaft 41 that has blade body 40 with intersecting activeedges 43 that subtend intersecting edge angle 44. As used herein, theterm “active edge” refers to a blade edge having a two or more conductoredges which transmit electrosurgery energy to tissue. In use, the bladeproduces the predetermined surgical effect (e.g., cutting) when theblade is moved through tissue in the direction indicated by arrow 42.This blade configuration moving through tissue 36 is illustrated in FIG.22. As the blade 40 moves through tissue, an electrosurgically affectedtissue region 16 is created. As the blade 40 moves through tissue 36,the leading corner 43 b initially contacts the tissue near the bottom ofthe blade and bottom edge 43 a then continues to supply electrosurgicalenergy to the already affected tissue as the blade is moved. Thus, thebottom active edge 43 a prolongs the residence time that the tissuealong bottom active edge 43 a is affected by electrosurgical energy. Theprolonged residence time increases smoke and eschar production andincreases tissue damage. The intersecting edge angle 44 influenceswhether such prolonged residence time occurs and the closer that theangle is to 180 degrees (i.e., the less there is a trailing edge) theless likely that prolonged residence time occurs. If the intersectingedge angle 44 is made more acute, the situation depicted in FIG. 23occurs. While the residence time of tissue near the trailing edge 45 isreduced in the configuration illustrated in FIG. 23, the trailing activeedge 45 following the incision does continue supplying electrosurgicalenergy to tissue 46 that has already been affected by electrosurgicalenergy delivered from the leading edge 43.

The intersecting active edges 43 in FIGS. 21-24 provide a point ofconcentration for electrosurgical energy when the blade first contactstissue 6 facilitating starting an electrosurgical effect such ascutting. Thus, such a concentration is desirable because it makesstarting or controlling the electrosurgical effect easier. In variousembodiments, the intersecting active edges angle does not allow theblade to be oriented during use that tissue is exposed to an active edge(and thus exposed to electrosurgical energy) for a prolonged residencetime. In some embodiments, the intersecting edge angle is obtuse, insome embodiments the intersecting edge angle is greater than about 160degrees, and in an embodiment the intersecting edge angle isapproximately equal to about 180 degrees. The example embodimentgeometries illustrated in the figures show edges that are substantiallystraight. Other embodiments include edges that have one or more curves,such as edges comprised of one or more parts of ellipses, circles,parabolas, or hyperbolas, and edges composed of a multiplicity ofstraight sections as well as edges composed of one or more combinationsof straight sections and curves.

In an embodiment, only one active edge is present as illustrated in FIG.24. The single active edge 43 is also the leading edge 43 c that firsttransfers electrosurgical energy to tissue 6 producing theelectrosurgically affected tissue region 46. The trailing edge 43 d isnot a active edge, i.e., it does not transfer electrosurgical energy totissue because it does not have an exposed surface (conductor edge)capable of transferring electrosurgical energy to tissue. The bladeillustrated in FIG. 24 comes to a region 43 e where electrosurgicalenergy is concentrated when the blade first contacts tissue 36.

In various embodiments, the blade has one or more active edgesconfigured so that they cause electrosurgical energy to enter tissueonly at the time when the blade first encounters tissue that has not yetexperienced the predetermined electrosurgical effect. In someembodiments, the blade has one or more active edges configured so thatthey have a region that concentrates electrosurgical energy when theblade first contacts tissue, such as in a region that approximates apoint, and such blade has two or more active edges configured so thatthey cause electrosurgical energy to enter tissue only at the time whenthe blade first encounters tissue that has not yet had the predeterminedelectrosurgical affect occur. For embodiments where the blade is to beused as a scalpel for cutting and other electrosurgical functions, theembodiments may have two active edges that comes to a pointapproximately.

In various embodiments, the benefits of the bipolar blade are combinedwith the benefits provided by the blade geometry and material to providea bipolar blade that exhibits further reduced smoke and eschargeneration. An example embodiment of such a combination is illustratedin FIGS. 25A-C. Referring to FIG. 25A, the blade includes an activeelectrode 3, passive electrode 4, and return electrode 5 which taper tonarrow conductor edges 3 a, 4 a, 5 a. The conductor edges 3 a, 4 a, 5 aare formed where the electrodes emerge from the insulation 25 cover. Theexposed regions of the electrodes can vary and the lengths of the bladescan be stepped or otherwise made unique to facilitate producingelectrical contact surfaces. Referring to FIG. 25B, the electrodes canbe configured to provide an acute insulation angle 38. For example, asillustrated in FIG. 25B, electrodes 3 and 5 can be shaped with a convexshape in the taper. Additionally, the insulation 25 can be tapered withan convex shape. The combination of the tapers in the electrodes 3 and 5and the insulation 25 provides a narrow active edge 49 with an acuteinsulation angle 38 to facilitate flow of decomposition products fromthe active region. Another example illustrated in FIG. 25C includeselectrodes 3, 4 and 5 which are shaped with a linear (i.e., flat) taperto a narrow conductor edge. The insulation 25 also features a lineartaper to a narrow active edge 49 that features an acute insulation angle38. The inter-blade insulation 6 can be provided down to active edge 49to prevent a short circuit among electrodes 3, 4 and 5, and can betapered or not tapered.

By employing various embodiments, a higher crest factor electrosurgicalenergy can be used for the predetermined surgical effect of cuttingwithout excessive damage to tissue or generation of smoke or eschar.Crest factor is the ratio of peak voltage to the root mean square (RMS)voltage. During cutting, crest factors of less than about 5 andtypically less than about 3 are used. For a predetermined surgicaleffect of moderate coagulation crest factors of about 4 to 5 aretypically used. To achieve the predetermined surgical effect ofaggressive coagulation, crest factors greater than 8, typically of about9, are used. If cutting tissue is attempted with crest factors that aretoo high, the cutting effect will be very poor and blades that do notincorporate features of the various embodiments will immediatelyaccumulate large masses of adherent tissue that prevents further useuntil the blade is cleaned. Thus, the drawbacks of conventionalelectrosurgical blades prevent the use of high crest factors forcutting. By focusing electrosurgical energy and reducing the residencetime during which tissue is exposed to electrosurgical energy thevarious embodiments of the present invention allow use of higher crestfactors for cutting.

Using high crest factors for cutting enhances hemostasis. Enhancinghemostasis is particularly beneficial when the tissue being affected ishighly vascularized, such as the liver. One embodiment provides a bladethat cuts with enhanced hemostasis that comprises an insulatedconductive element that tapers to one or more conductor edges that areat least partially exposed such that they can transfer electrosurgicalenergy to tissue and that have thermal path conductance that is at least0.0002 W/° K, wherein the exposed edge is no thicker than about 0.005inches and the blade is connected to an ESU configured to supplyelectrosurgical power with a crest factor of 5 or larger.

In various embodiments, the outer insulating layer may have a maximumthermal conductance of about 1.2 W/cm²° K when measured at about 300° K,preferably about 0.12 W/cm²° K or less when measured at about 300° K,and more preferably about 0.03 W/cm²° K when measured at about 300° K.As used herein, thermal conductance refers to a measure of the overallthermal transfer across any given cross section (e.g. of the insulationlayer), taking into account both the thermal conductivity of thematerials comprising such layer and the thickness of the layer (i.e.thermal conductance of layer=thermal conductivity of material comprisingthe layer (W/cm° K)/thickness of the layer (cm)).

In relation to the various embodiments, the insulation layer should alsoexhibit a dielectric withstand voltage of at least the peak-to-peakvoltages that may be experienced by the electrosurgical instrumentduring surgical procedures. The peak voltages will depend upon thesettings of the RF source employed, as may be selected by clinicians forparticular surgical procedures. In various embodiments, the insulationlayer should exhibit a dielectric withstand voltage of at least about 50volts, and more preferably, at least about 150 volts. As used herein,the term “dielectric withstand voltage” means the capability to avoid anelectrical breakdown (e.g. an electrical discharge through theinsulating layer) for electrical potentials up to the specified voltage.

In some embodiments, the insulating or electrode bonding layer maycomprise a porous ceramic material that has had at least the pores onthe surface sealed to prevent or impede the penetration of biologicalmaterials into the pores. Such ceramic may be applied to the electrodesvia dipping, spraying, etc, followed by curing via drying, firing, etc.Preferably, the ceramic insulating layer should be able to withstandtemperatures of at least about 2000° F.

The ceramic insulating layer may comprise various metal/non-metalcombinations, including for example compositions that comprise thefollowing: aluminum oxides (e.g. alumina and Al₂O₃), zirconium oxides(e.g. Zr₂O₃), zirconium nitrides (e.g. ZrN), zirconium carbides (e.g.ZrC), boron carbides (e.g. B₄C), silicon oxides (e.g. SiO₂), mica,magnesium-zirconium oxides (e.g. (Mg—Zr)O₃), zirconium-silicon oxides(e.g. (Zr—Si)O₂), titanium oxides (e.g., TiO₂) tantalum oxides (e.g.Ta₂O₅), tantalum nitrides (e.g. TaN), tantalum carbides (e.g., TaC),silicon nitrides (e.g. Si₃N₄), silicon carbides (e.g. SiC), tungstencarbides (e.g. WC) titanium nitrides (e.g. TiN), titanium carbides(e.g., TiC), nibobium nitrides (e.g. NbN), niobium carbides (e.g. NbC),vanadium nitrides (e.g. VN), vanadium carbides (e.g. VC), andhydroxyapatite (e.g. substances containing compounds such as 3Ca₃ (PO₄)₂Ca(OH)₂ Ca₁₀(PO₄)₆ (OH)₂ Ca₅(OH)(PO₄)₃, and Ca₁₀H₂O₂₆P₆). One or moreceramic layers may be employed, wherein one or more layers may beporous, such as holes filled with one or more gases or vapors. Suchporous compositions will usually have lower thermal conductivity thannonporous materials. An example of such materials is foam, such as anopen cell silicon carbide foam. Such porous materials have thedisadvantage that they allow fluids, vapors, or solids to enter thepores whereby they are exposed to prolonged contact with hightemperatures which can lead to thermal decomposition or oxidation andproduce smoke or other noxious or possibly dangerous materials. Sealingthe surface of the ceramic prevents such incursions, while substantiallypreserving the beneficial reduced thermal conductivity of the pores.

Ceramic coatings or electrode bonding materials may also be formed inwhole or part from preceramic polymers that when heated form materialscontaining Si—O bonds able to resist decomposition when exposed totemperatures in excess of 1200° F., including compositions that use oneor more of the following as preceramic polymers: silazanes,polysilzanes, polyalkoxysilanes, polyureasilazane, diorganosilanes,polydiorganosilanes, silanes, polysilanes, silanols, siloxanes,polysiloxanes, silsesquioxanes, polymethylsilsesquioxane,polyphenyl-propylsilsesquioxane, polyphenylsilsesquioxane,polyphenyl-vinylsilsesquioxane. Preceramic polymers may be used to formthe ceramic coating by themselves or with the addition of inorganicfillers such as clays or fibers, including those that contain siliconoxide, aluminum oxides, magnesium oxides, titanium oxides, chromeoxides, calcium oxides, or zirconium oxides.

Ceramic coatings may also be formed by mixing one or more colloidalsilicate solutions with one or more filler materials such as one or morefibers or clays. The filler materials can contain one or more materialsthat have at least 30 percent by weight Al₂O₃ or SiO₂ either alone orcombined with other elements, such occurs in kaolin or talc. Thecolloidal silicate and filler mixture may optionally contain othersubstances to improve adhesion to electrode surfaces or promoteproducing a sealed or hydrophobic surface. Representative examples ofcolloidal silicate solutions are alkali metal silicates, including thoseof lithium polysilicate, sodium silicate, and potassium silicate, andcolloidal silica. Fibers may include those that contain in part orwholly alumina or silica or calcium silicate, and Wollastonite. Claysmay include those substances that are members of the smectite group ofphyllosilicate minerals. Representative examples of clay mineralsinclude bentonite, talc, kaolin (kaolinite), mica, clay, sericite,hectorite, montmorillonite and smectite. Various embodiments use atleast one of kaolin, talc, and montmorillonite. These clay minerals canbe used singly or in combination. In various embodiments, at least onedimension, such as diameter or particle size, of at least one of thefiller materials has a mean value of less than 200 micrometers and morepreferably has a mean value of less than 50 micrometers and even morepreferably has a mean value of less than 10 microns and still morepreferably has a mean value less than 5 microns Substances that may beadded to promote adhesion or production of a sealed or hydrophobicsurface include those that increase the pH of the mixture, includingsodium hydroxide or potassium hydroxide, and hydrolysable silanes thatcondense to form one or more cross-linked silicone-oxygen-siliconstructures.

Sealing a porous insulator is accomplished not by coating the ceramic inthe sense that electrosurgical accessories have been coated with PTFE,silicone polymers and other such materials. Best surgical performanceoccurs when accessories are thin, therefore pores are best filled by amaterial that penetrates the surface of the porous material and sealsthe pores. Some residual material may remain on the surface, but suchmaterial is incidental to the sealing process.

Sealing materials need to withstand temperatures exceeding 400° F. andmore preferably withstand temperatures exceeding 600° F. Silicates andsolutions containing or forming silicates upon curing can be used. Othermaterials may be used, including silicone and fluorosilicones. Forsealing, the materials need to have low viscosity and other propertiesthat enable penetration into the surface of the porous insulator.Traditional silicone and fluorosilicone polymer-forming compounds do nothave these properties unless they are extensively diluted with athinning agent, such as xylene or acetone.

A sealed porous insulation may be employed to yield an average maximumthermal conductivity of about 0.006 W/cm-° K or less where measured at300° K. The insulating layer outside of the blade may have a thicknessof between about 0.001 and 0.2 inches, preferably between about 0.005and 0.100 inches and more preferably between about 0.005 and 0.050inches.

A coating that is applied as a single substance that upon curing doesnot require sealing may also be used for the outer insulation or as thebonding material between electrodes. Examples of such coatings includethose formed from mixtures that use one or more of the aforementionedcolloidal silicates and clays and also use one or more substances thatreduce the surface free energy of the surface. Substances that reducethe surface free energy include: halogenated compounds, fluoropolymercompounds, such as PTFE and PFA, including aqueous dispersions of suchcompounds; and organofunctional hydrolysable silanes, including thosecontaining one or more fluorine atoms on one or more pendant carbonchains.

In some embodiments, a hydrolysable silane is a component in the coatingor in the insulating material between electrodes, with the hydrolysablesilane having one or more halogen atoms and having a general formula ofCF₃(CF₂)_(m)(CH2)_(n)Si(OCH₂CH₃)₃ where m is preferably less about 20and more preferably about 5 or less and where n is preferably about 2.Other groups besides (OCH₂CH₃)₃, such as those based on ethyl groups,may be used and fall within the scope of the various embodiments whenthey also are hydrolysable. Other halogens, such as chlorine, may besubstituted for the fluorine, although these will typically produceinferior results.

Preferably, the surface energy (also referred to as the surface tensionor the surface free energy) of the coating is less than about 32millinewtons/meter and more preferably less than about 25millinewtons/meter and even more preferably less than about 15millinewtons/meter and yet more preferably less than about 10millinewtons/meter.

In an embodiment, the conductive elements or conductor edges or both ofthe electrosurgical instrument may be configured to have a thermalconductivity of at least about 0.35 W/cm° K when measured at about 300°K. By way of example, the conductive elements or conductor edges or bothmay comprise at least one metal selected from the group including:silver, copper, aluminum, gold, tungsten, tantalum, columbium (i.e.,niobium), and molybdenum. Alloys comprising at least about 50% (byweight) of such metals may be employed, and even more preferably atleast about 90% (by weight). Additional metals that may be employed insuch alloys include zinc.

In various embodiments, at least a portion of the conductor edge is notinsulated (i.e. not covered by the outer insulating layer). Inconnection therewith, when the conductor edge comprises copper, theexposed portion may be coated or plated (e.g. about 10 microns or less)with a biocompatible metal. By way of example, such biocompatible metalmay be selected from the group including: nickel, silver, gold, chrome,titanium tungsten, tantalum, columbium (i.e., niobium), and molybdenum.

In some embodiments, the conductive element, conductor edge, or both maycomprise two or more layers of different materials. More particularly,at least a first metal layer may be provided to define at least part ofthe conductor edge that is functional to convey electrosurgical energyto tissue as described above. Such first metal layer may comprise ametal having a melting temperature greater than about 2600° F.,preferably greater than about 3000° F., and more preferably greater thanabout 4000° F., thereby enhancing the maintenance of a desiredperipheral edge thickness during use (e.g. the outer extreme edge notedabove). Further, the first metal layer may have a thermal conductivityof at least about 0.35 W/cm° K when measured at 300° K.

For living human/animal applications, the first metal layer may comprisea first material selected from a group including: tungsten, tantalum,columbium (i.e., niobium), and molybdenum. All of these metals havethermal conductivities within the range of about 0.5 to 1.65 W/cm° Kwhen measured at 300° K. Alloys comprising at least about 50% by weightof at least one of the group of materials may be employed, and morepreferably at least about 90% by weight.

In addition to the first metal layer, the conductive element may furthercomprise at least one second metal layer on the top and/or bottom of thefirst metal layer. A first metal layer as noted above can be provided ina laminate arrangement between top and bottom second metal layers. Toprovide for rapid heat removal, the second metal layer(s) preferably hasa thermal conductivity of at least about 2 W/cm° K. By way of example,the second layer(s) may advantageously comprise a second materialselected from the group including: copper, gold, silver and aluminum.Alloys comprising at least about 50% of such materials may be employed,and preferably at least about 90% by weight. It is also preferable thatthe thickness of the first metal layer and of each second metal layer(e.g. for each of a top and bottom layer) be between about 0.001 and0.25 inches, and even more preferably between about 0.005 and 0.1inches.

One or more of the conductor edges may be plated with gold or silver oralloys thereof to confer added oxidation resistance to the portions ofthe electrodes exposed to tissue or current flow or both. Such platingmay be applied using electroplating, roll-bonding or other means eitherafter assembly or prior to assembly of the electrodes to form blades.The plating thickness can be at least about 0.5 micrometers andpreferably at least about 1 micrometer.

As may be appreciated, multi-layered metal bodies of the type describedabove may be formed using a variety of methods. By way of example,sheets of the first and second materials may be roll-bonded togetherthen cut to size. Further, processes that employ heat or combinations ofheat and pressure may also be utilized to yield a laminated electrode.

In some embodiments, the electrosurgical instrument may further comprisea heat sink for removing thermal energy from the conductor edge,conductive element, or both. In this regard, the provision of a heatsink helps establishes a thermal gradient for conducting heat away fromthe conductor edge, thereby reducing undesired thermal transfer to atissue site. More particularly, it is preferable for the heat sink tooperate so as to maintain the maximum temperature on the outside surfaceof the insulating layer at about 160° C. or less, more preferably atabout 80° C. or less, and most preferably at 60° C. or less. Relatedly,it is preferable for the heat sink to operate to maintain an averageconductive element temperature of about 500° C. or less, more preferablyof about 200° C. or less, and most preferable of about 100° C. or less.

In an embodiment, the heat sink may comprise a vessel including a phasechange material that either directly contacts a portion of theelectrodes (e.g. a support shaft portion) or that contacts a metalinterface provided on the vessel which is in turn in direct contact witha portion of the electrodes (e.g. a support shaft portion). Such phasechange material changes from a first phase to a second phase uponabsorption of thermal energy from the electrodes. In this regard, thephase change temperature for the material selected should preferably begreater than the room temperature at the operating environment andsufficiently great as to not change other than as a consequence ofthermal heating of the electrosurgical instrument during use. Such phasechange temperature should preferably be greater than about 30° C. andmost preferably at least about 40° C. Further, the phase changetemperature should be less than about 225° C. Most preferably, the phasechange temperature should be less than about 85° C.

The phase change may be either from solid to liquid (i.e., the phasechange is melting) or from liquid to vapor (i.e., the phase change isvaporization) or from solid to vapor (i.e., the phase change issublimation). More practical phase changes to employ are melting andvaporization. By way of example, such a phase change material maycomprise a material that is an organic substance (e.g., fatty acids,such as stearic acid, hydrocarbons such as paraffins) or an inorganicsubstance (e.g., water and water compounds containing sodium, such as,sodium silicate (2-)-5-water, sodium sulfate-10-water).

In an embodiment, the heat sink may comprise a gas flow stream thatpasses in direct contact with at least a portion of the electrodes. Suchportion may be a peripheral edge portion and/or a shaft portion of theelectrodes that is designed for supportive interface with a holder forhand-held use. Alternatively, such portion may be interior to at least aportion of the electrodes, such as interior to the exposed peripheraledge portion and/or the shaft portion of the electrodes that is designedfor supportive interface with a holder for hand-held use. In yet otherembodiments, the heat sink may simply comprise a thermal mass (e.g.disposed in a holder).

In an embodiment, an electrosurgical instrument comprises a main bodyportion having a blade-like configuration at a first end and anintegral, approximately cylindrical shaft at a second end. The main bodymay comprise a highly-conductive metal and/or multiple metal layers asnoted. At least a portion of the flattened blade end of the main bodycan be coated with a ceramic-based and/or silicon-based, polymerinsulating layer, except for the peripheral edge portion thereof. Thecylindrical shaft of the main body can be designed to fit within anouter holder that can be adapted for hand-held use by medical personnel.Such holder may also include a chamber comprising a phase-changematerial or other heat sink as noted hereinabove. Additionally, one ormore control elements, such as buttons or switches, may be incorporatedinto the holder for selectively controlling power or other aspects ofthe device's operation, such as the application of one or more,predetermined, electrosurgical signal(s) from an RF energy source to theblade via the shaft of the main body portion.

In some embodiments, the active, return and passive electrodes withtheir surrounding insulation are provided as a single use or disposableblade that can be coupled to a holder or handle which may be reusable ora single use device. In such embodiments, the blade includes electricalconnector surfaces on the proximal end (i.e., the end of the electrodesclosest to the handle in use) suitable for electrically connecting eachof the active, return and passive electrodes to compatible electricalconnector surfaces in the handle, such as sleeve contactors within theholder or handle. The connector surfaces may also serve as a mechanicalcoupling so that by inserting the blade unit into the holder connector,the blade unit is rigidly held by the holder. In such embodiments, theholder or handle may include one or more control components, such asbuttons or switches, for selectively controlling power or other aspectsof the device's operation, such as controlling the application of one ormore, predetermined, electrosurgical signal(s) from an RF energy sourceto the blade via the shaft of the main body portion. In such anembodiment, the disposable blade unit can be sealed in a sterilepackage, which may include instructions for assembly and use, to providean electrosurgical kit to be opened at the time surgery is to beperformed.

In some embodiments, the blade 40, including its active, return andpassive electrodes with their surrounding insulation, is fixedly coupledto a holder or handle 51 as a single use disposable electrosurgicalassembly 50, such as illustrated in FIG. 26. In such embodiments, thedisposable electrosurgical assembly 50 includes a blade 40 mechanicallyand electrically coupled to the handle 51, such as by a connector 52. Anelectrical connector 53 on the handle 51 can be provided to connect,such as by means of a cable 59, to an ESU or similar source of radiofrequency (RF) AC power. An internal set of conductors 54 conduct RFpower from the connector 53 at one end of the handle 51 to theblade-to-holder connector 52 at the other end of the handle 51. Theinternal conductors 54 and the blade-to-handle connector 52 includeseparate electrical paths and are configured to connect the RF power andconnect a negative voltage source to each of the active and returnelectrodes and connect a positive voltage source to the passiveelectrode. In an embodiment, the electrical connector 53 and cable 59may also connect the handle 51 to a DC power source for providing anegative voltage for connection to the active and return electrodes anda positive voltage for connection to the passive electrode by way of theinternal conductors 54 and the blade-to-handle connector 52. In anembodiment, the handle 51 includes a rectifier circuit, such asdescribed herein, connected to the internal conductors 54 or electricalconnector 53 to receive RF power and output DC current with the negativevoltage provided to the active and return electrodes and the positivevoltage provided to the passive electrode by way of the blade-to-handleconnector 52. Electrical and thermal insulation 55 can be provided toisolate power being conducted in the internal conductor 54 from thehandle exterior 56, thereby protecting the clinician using thedisposable electrosurgical assembly 50. The blade connector 52 may alsoinclude electrical insulation to electrically isolate the blade 40 fromthe handle exterior 56. Control elements 57, 58 may be provided on thehandle 51 to enable a user to activate, deactivate and otherwise controlpower provided by the ESU or RF power source. The handle 51 may beshaped to enable a user to comfortably hold or otherwise manipulate theassembly, provided with a surface material or surface texture, such asroughening, to enhance a user's grip and other ergonomic features to aida clinician in manipulating the disposable electrosurgical assembly 50.A cable 59 connectable to the connector 53 and fitted with a suitableelectrical plug 60 can be used to electrically couple the assembly 50 toan ESU. The cable 59 may be reusable or disposable. In an embodiment,the cable 59 and plug 60 are included as part of the assembly 50. In anembodiment including one or more control elements 57, 58 on the handle51, electronic connectors may be provided within cable 59 for relayingcontrol signals to the ESU.

In some embodiments, a single use sterile disposable electrosurgicalassembly 50 can be sealed in a sterile package, which may include acable 59 and/or instructions for assembly and use, to provide anelectrosurgical kit to be opened at the time surgery is to be performed.

Conventional electrosurgical signals may be advantageously employed incombination with one or more of the above-noted electrosurgicalinstrument embodiments. In particular, the inventive electrosurgicalinstrument yields benefits when employed with electrosurgical signalsand associated apparatus of the type described in U.S. Pat. No.6,074,387, hereby incorporated by reference in its entirety.

The apparatus and methods for reducing smoke, eschar, and tissue damageaccording to various embodiments may be applied in conjunction withother methods for reducing the local heating that promotes the excessiveelectrosurgical tissue decomposition which leads to smoke, eschar, andtissue damage. Such additional methods for reducing local heatinginclude providing for an effective level of heat removal away fromfunctional portions of an electrosurgical instrument and/or by otherwiseenhancing the localized delivery of an electrosurgical signal to atissue site, such as by reducing the exposed areas of either or bothfunctional and nonfunctional areas by using thermal insulation.

While the present invention has been disclosed with reference to certainpreferred embodiments, numerous modifications, alterations, and changesto the described embodiments are possible without departing from thesphere and scope of the present invention, as defined in the appendedclaims. Accordingly, it is intended that the present invention not belimited to the described embodiments, but that it have the full scopedefined by the language of the following claims, and equivalentsthereof.

1. An electrosurgical instrument for conveying electrosurgical power totissue to achieve a predetermined electrosurgical effect, comprising: anactive electrode having a first section and a first tapered sectionterminating at a first conductor edge; a first insulation layer having asecond tapered section overlaying the active electrode which tapers on aside of the first tapered section to expose the first conductor edge; areturn electrode electrically isolated from the active electrode, thereturn electrode having a third section and a third taper sectionterminating at a second conductor edge; and a second insulation layerhaving a fourth tapered section overlaying the return electrode whichtapers on a side of the third tapered section to expose the secondconductor edge; and a passive electrode electrically isolated from theactive electrode and the return electrode.
 2. The electrosurgicalinstrument as recited in claim 1, wherein at least a portion of thethickness of the first conductor edge is less than that of the firstsection.
 3. The electrosurgical instrument as recited in claim 2,wherein at least a portion of the first conductor edge is flush with thefirst insulating layer near the first conductor edge.
 4. Theelectrosurgical instrument as recited in claim 3, wherein at least aportion of the first tapered section includes a beveled surface.
 5. Theelectrosurgical instrument as recited in claim 4, wherein at least aportion of the first tapered section includes two beveled surfaces. 6.The electrosurgical instrument as recited in claim 5, wherein at least aportion of the first tapered section has a concave shape.
 7. Theelectrosurgical instrument as recited in claim 6, wherein at least aportion of the second tapered section has a concave shape.
 8. Theelectrosurgical instrument as recited in claim 7, wherein at least aportion of the third tapered section has a concave shape.
 9. Theelectrosurgical instrument as recited in claim 8, wherein at least aportion of the fourth tapered section has a concave shape.
 10. Theelectrosurgical instrument as recited in claim 6, wherein at least aportion of the second tapered section insulation layer has a lineartaper shape
 11. The electrosurgical instrument as recited in claim 8,wherein at least a portion of the fourth tapered region has a lineartaper shape.
 12. The electrosurgical instrument as recited in claim 1having an insulation angle less than about 60 degrees.
 13. Theelectrosurgical instrument as recited in claim 1 having an insulationangle less than about 45 degrees.
 14. The electrosurgical instrument asrecited in claim 1 having an insulation angle less than about 20degrees.
 15. The electrosurgical instrument as recited in claim 1,wherein each of the first and second conductor edges has a thermalconductivity of at least 0.0002 W/° K at about 300° K.
 16. Theelectrosurgical instrument as recited in claim 1, wherein at least aportion of the first conductor edge has a transverse cross section thatcomes to approximately a point.
 17. The electrosurgical instrument asrecited in claim 16, wherein at least a portion of the second conductoredge has a transverse cross section that comes to approximately a point.18. The electrosurgical instrument as recited in claim 1, wherein atleast a portion of the first conductor edge has a transverse crosssection that forms an acute angle.
 19. The electrosurgical instrument asrecited in claim 18, wherein at least a portion of the second conductoredge has a transverse cross section that forms an acute angle.
 20. Theelectrosurgical instrument as recited in claim 1, wherein at least aportion of the first conductor edge has a thickness less than about0.005 inches.
 21. The electrosurgical instrument as recited in claim 1,wherein at least a portion of the first conductor edge has a thicknessless than about 0.002 inches.
 22. The electrosurgical instrument asrecited in claim 1, wherein at least a portion of the first conductoredge has a thickness less than about 0.0005 inches.
 23. Theelectrosurgical instrument as recited in claim 1, wherein at least aportion of the thickness of the insulation layer within a primaryreaction region is at least one half the thickness of either the firstor second conductor edge.
 24. The electrosurgical instrument as recitedin claim 1, wherein the thickness of the first insulation layer aprimary reaction region is at least as thick as the first conductoredge.
 25. The electrosurgical instrument as recited in claim 2, whereinthe ratio of width of a first section to at least a portion of the firstconductor edge is at least 5:1
 26. The electrosurgical instrument asrecited in claim 2, wherein the ratio of width of a first section to atleast a portion of the first conductor edge is 20:1
 27. Theelectrosurgical instrument as recited in claim 3, wherein at least oneside of the first tapered section extends radially inward.
 28. Theelectrosurgical instrument as recited in claim 27, wherein at least oneside of the third tapered section extends radially inward.
 29. Theelectrosurgical instrument as recited in claim 28 having an insulationangle less than about 45 degrees.
 30. The electrosurgical instrument asrecited in claim 28, having an insulation angle less than about 20degrees.
 31. The electrosurgical instrument as recited in claim 1,further comprising a holder electrically and mechanically coupled as aunit to the active electrode and the return electrode, the holdercomprising: a connector for electrically connecting the holder to asource of radio frequency power; and an electrical connector configuredto electrically couple the active electrode and return electrode toradio frequency power and a negative voltage source and couple thepassive electrode to a positive voltage source.
 32. The electrosurgicalinstrument as recited in claim 31, further comprising a connector forelectrically connecting the holder to the source of radio frequencypower.
 33. The electrosurgical instrument as recited in claim 31,further comprising a rectifier circuit configured to receive the radiofrequency power and provide the source of negative and positive voltage.34. The electrosurgical instrument as recited in claim 33, wherein therectifier circuit is positioned within the holder.
 35. Theelectrosurgical instrument as recited in claim 33, further comprising aradio frequency generator configured to provide the source of radiofrequency power.
 36. An electrosurgical instrument for conveyingelectrosurgical power to tissue to achieve a predeterminedelectrosurgical effect comprising: an electrosurgical blade, theelectrosurgical blade comprising an active electrode having a firstsection and a first tapered section terminating at a first conductoredge, a first insulation layer having a second tapered sectionoverlaying the active electrode which tapers on a side of the firsttapered section to expose the first conductor edge, a return electrodeelectrically isolate from the active electrode, the return electrodehaving a third section and a third taper section terminating at a secondconductor edge, and a second insulation layer having a fourth taperedsection overlaying the return electrode which tapers on a side of thethird tapered section to expose the second conductor edge; a passiveelectrode electrically isolated from the active electrode and the returnelectrode; and a handle coupled to the electrosurgical blade.
 37. Theelectrosurgical instrument as recited in claim 36, further comprising anelectrical couple unit which couples the electrosurgical instrument to aradio frequency power source.
 38. The electrosurgical instrument asrecited in claim 36, wherein the handle houses a coupling mechanism tosecurely and electrically couple the electrosurgical instrument to thehandle.
 39. The electrosurgical instrument as recited in claim 38,further wherein the coupling mechanism also couples the active electrodeand the return electrode to a radio frequency power source and to anegative voltage source and couples the passive electrode to a positivevoltage source.
 40. The electrosurgical instrument as recited in claim37, wherein the coupling mechanism selectively releases theelectrosurgical instrument.
 41. The electrosurgical instrument asrecited in claim 36, further comprising a radio frequency (RF) powersource electrically coupled to the active electrode and the returnelectrode; and a DC voltage source providing a negative voltage coupledto the active electrode and the return electrode and a positive voltagecoupled to the passive electrode.
 42. The electrosurgical instrument asrecited in claim 41, wherein the DC voltage source comprises a rectifiercircuit configured to receive RF power from the RF power source andoutput the negative voltage and the positive voltage.
 43. Theelectrosurgical instrument as recited in claim 42, wherein the rectifiercircuit is positioned within the handle.
 44. A sterile package kit foruse in performing an electrosurgical procedure, comprising: a sterilepackage; and an electrosurgical instrument sealed within the sterilepackage, the electrosurgical instrument comprising: an active electrodehaving a first section and a first tapered section terminating at afirst conductor edge; a first insulation layer having a second taperedsection overlaying the active electrode which tapers on a side of thefirst tapered section to expose the first conductor edge; a returnelectrode electrically isolate from the active electrode, the returnelectrode having a third section and a third taper section terminatingat a second conductor edge; a second insulation layer having a fourthtapered section overlaying the return electrode which tapers on a sideof the third tapered section to expose the second conductor edge; apassive electrode electrically isolated from the active electrode andthe return electrode; and a handle sealed within the sterile package andelectrically coupled to the active, return and passive electrodes. 45.The sterile package kit according to claim 44, further comprising anelectrical connector coupled to the handle and configured toelectrically couple the electrosurgical instrument to a radio frequency(RF) power source.
 46. The sterile package kit according to claim 44,further comprising a rectifier circuit configured to receive RF powerand output a negative and a positive DC voltage.
 47. The sterile packagekit according to claim 46, wherein the rectifier circuit is positionedwithin the handle and the handle is configured to provide the negativeDC voltage to the active and return electrodes and positive DC voltageto the passive electrode.
 48. The sterile package kit according to claim44, further comprising printed instructions informing a user how tocouple the electrosurgical instrument to the RF power source.